Stress (high levels of cortisol) destroy collagen whereever it is found in the body: in the skins dermis,
in the lining of your gut, the cartillage in your joints, your neck, your back, your bone - many of the places where POISers experience problems.
Collagen supplements can aid in healing the gut which teoretically gives hughe improvements for POISers. I dont see why collagen is the cause of your hairloss in your case. Maybe it just coincided with the supplemantation of collagen.
Male hair loss is caused by heavy physical stress in combination with heritage and sedimentary lifestyle (about 40 % of all POISers are "desktop-based" engineers, according to a poll here), bad sleep, high sugar intake and other things that ruins the hormonal balance and masculinism. Its not the testosterone that cause hair loss, its rather the lack of blood and oxygen supply to the hair follicles and wrong pH balance in the skin dermis which accelerates the conversion from testosterine to DHT (dihydrotestosterone).
By the way, POIS cannot "be cured" by taking a regulary "pill" because of simple logic:
1. If your taking a pill regulary to be free from symptoms, your not cured, are you!?
2. If the cause has something to do with things like stress, sedimenray lifestyle, bad sleep or lack of excercise, a pill cant "cure" any of that (unless it makes you a zombie).
Sollution:Relax, destress, yoga, mindfulness, meditation blah blah blah...
Exersice
Improve sleep (go to bed earlier, wake up earlier, get sunshine in the morning, excercise, no computer/screen work late, lower lights in home at evening ...)
Eat collagen, boneboroth, glutamine
Go for a paleo diet
Stay away from sugar
Supplement with vitamin C,A,D,E,B-complex, iron, zink and magnesium + an all-inclusive vitamin/mineral pill.
Keep your mother-in-law at a healthy distance.