Feeling strange after travel? it would help to know what your symptoms are, though what I recall from our our (brief) discussion was that it seemed you were experiencing symptoms that seemed unusual or hard to pinpoint and/or describe(?) If that's the case then I have an intuition that this information may be helpful. I hope you feel better soon!
When we don't know what specifically our malaise is or where it comes from, then it's best to consider/examine the possible sources. In the attempt to identify (and learn how to manage, and hopefully fix) my Chronic Fatigue Syndrome (itself a 'mystery illness') I have researched a wide gamut of possible threats to our biological entity and systems - as well as studied associated proposed healing modalities.
What I have found is that there are internal and external threats and factors. The external factors I break down into pathogens and toxic substances. Pathogens I then break down into: Virus; Bacteria; Fungus/Mold; Parasites; Myocoplasma; Spirochites (and possibly pleromorphs and retroviruses).
The toxic substances category include many and varied sources including: heavy metals; pesticides/fungicides; phtalates; food additives/dyes/preservatives; a huge list of hormone disrupting chemicals (including BPA, dioxins, atrazine, perchlorate, bromine, perfluorinated chemicals, glycol ethers, arsenic, alkylphenol, Parabens, etc.); volotile organic compounds (VOC's) (sources including cosmetics, asbestos from non -US made laundry machine belts, dryer sheets, dust, chemical solvents, cleaning products, aspartame, plastics run in dishwasher, offgasing of automotive plastic and mattresses, unshielded microwaves, smartgrid pings, chlorine in shower both absorbed by skin and inhaled as vapor ).
Internal factors may include: one's psychology (being generally at ease and content, versus experiencing stress); diet (getting enough vitamin b12, etc.); sunlight exposure (vitamin D); microbiome balance; hormonal balance; immune system; exercise/flexibility (exercise because our glands only circulate hormones when we are moving, and mostly with up and down motion), etc.
Our microbiome is important as it interacts and affects many biological systems (our immune system; digestive; central nervous system; hormonal system; and psychology/psychobiology). Many attest that fixing one's gut is key. Adressing this includes varied methods such as: drinking bone broth; use of Xifaxan (a perscription medicine); reintroducing probiotics by eating raw organic leafy greens (lightly washed in tapwater and not consuming prewashed/precut packaged greens - as they are first rinsed in chlorine before water, which destroys probiotic microcolonies). The leaves (preferably chard or kale) fold over and protect the colonies as they make their way to the small intestine, where they are needed most (this works considerably better than consuming cheese, yogurt or probiotic capsules). Drinking raw juiced celery before anything in the morning introduces salts required for production of the six types of hydrochloric acid required for digestion.
Regular doctors aren't always able to help, as they often don't have time to keep up on the latest research (especially regarding obscure or 'mystery illnesses'). In fact, there is a 7 to 15 year gap between discoveries published in medical journals and the resulting implementation in practice. Sometimes private specialists or clinics have better insight (but that is costly). To add to the confusion is that there are different kinds of doctors (allopathic; naturopathic; aryuvedic; osteopathic; tcm, etc.).
As testing is expensive, and clinics that specialize in abstruce illnesses are also expensive, I have found it best to do one's own research then find a doctor within the healthcare insurance system who is willing to listen to the latest studies and consider 'alternative' treatment. For example, I found a powerful chemotherapy drug that has cured many chronic fatigue syndrome patients and my doctor is willing to let me try it (however, I am attempting to find alternatives!).
I recommend to first look at anything that has changed in your environment (new apartment, new diet, etc.). In this case you traveled somewhat recently. As equatorial regions have more and different types parasites than here, it is possible that you have been exposed to them.
By the time we are in our 20's, we all harbor parasites. It seems not uncommon to 'pick them up' during a voyage, and perhaps this is because we're exposed to ones our system hasn't responded to before?
According to the theory of social evolution, for example, the reason why birds in tropics have such colorful plumage is because of the higher abundance of parasites in that climate. The plumage signals to prospective mates that - not only are they able to efficiently find food, but that they have the genes that successfully ward off (or manage) parasites - allowing excess energy to be divested to the colorful feathers. The theory gets more interesting from there (I recommend checking out Professor Robert Triver's work).
The problem with testing for them is that the tests only detect between 5%-15% of known parasites. There is a controversial test done by Igenix in Sacramento that has better detection rates (samples are analyzed under a microscope) but it is costly and they have been known for false positives (though I wouldn't entirely rule them out as an resource).
Symptoms of parasite infection vary tremendously. Also, they mimic other exposures/diseases (such as heavy metal toxicity, etc.). The following I quickly grabbed from an article called '21 Signs You Might Have a Parasite (And What To Do About It)' https://blog.paleohacks.com/signs-you-have-a-parasite-and-what-to-do-about-it/#
"Not feeling quite right? Parasites can be the actual cause of most mysterious illnesses. Some people may not have any symptoms from infection. Yet, these are some of the most commonly associated symptoms with a parasite infection:
Mood disorders
Strong cravings for processed and sugary foods
Anemia or iron deficiency (worms can create enough blood loss to cause anemia or iron deficiency)
Skin ailments such as hives, rashes, weeping eczema, itchy dermatitis, acne, ulcers, sores, lesions, etc.
Recurring yeast infections like Candida
Bleeding gums
Headaches
Anxiety
Nervousness
Teeth grinding and drooling during sleep
Food allergies/food sensitivities
Loss of appetite
Sexual dysfunction
Chronic fatigue
Unhealthy food cravings
Persistent digestive problems (cramps, bloating, gas, etc.)
Hungry all the time
Sore/stiff joints
Breathing problems
Itching – especially around mouth, nose and anus
Memory problems"
There are different ways of dealing with them: I have read about water fasts where they were able to see parasites exiting (I won't explain this gross process); I've read about devices to zap them with electricity (such as the Royal Riffe machine, or Huda Clark's machine, both of which are highly controversial); I've read about special cleanses and/or enemas (gross); and finally I settled on trying rainforest herbs in capsules. Often I'll read studies that have been conducted (on particular medicines or herbs, for instance) as well as read comments from people who've tried the medicines or various products. I had read many studies showing tremendous effects with graviola and that's how I came across (and ordered) the product: 'Rainforest Pharmacy Amazon A-P' https://www.rainpharm.com/amazon-formulas/amazon-a-p.html?limit=all
From there I found and purchased the identical: 'Raintree Formulas Amazon A-P 650mg 120 Veg Capsules Antiparasitic Nutrition' https://www.amazon.com/Raintree-Formulas-Capsules-Antiparasitic-Nutrition/dp/B00DSTUNR0
The ingredients are a blend of amargo, simarouba, boldo, fedegoso, carqueja, quinine, erva tostao, epazote, anamu, and graviola. Rainforest Pharmacy and Raintree both make other products as well (to combat viruses, another against fungus, etc.).
I had also read studies regarding wormwood as an anti parasitic, which led me to the product: ParaCleanse - Black Walnut & Wormwood - by Dr Hulda Clark https://www.amazon.com/ParaCleanse-Black-Walnut-Wormwood-Hulda/dp/B01M63CDZW (Disclaimer, Dr Clark is fringe and kookie, but that doesn't mean this product is or isn't viable).
I hope that helps :)