I've been on Propecia (actually on a 1/4 pill of Proscar) for a few years now, with success. It had stopped more hair from falling out than had already happened.
I visited India recently for a full 2 months, and continued taking the Proscar and had no issues. Since I've been back (about 4 weeks now) and especially during the past 3 weeks, I've noticed hair falling out while shampooing / towel drying / in the sink. Unfortunately I didn't make much of it until this weekend, when I took a closer look and realized that at this rate it's all going to be gone in another 3 weeks!
I only missed a couple of doses here and there in India, which my dermatologist has told me is okay once in a while(?) Also, I find it surprising that my hair survived years of styling product / straightening iron, and now that I've stopped using much product and straightening it, since I've been back from my trip, it's started falling out.
My diet is pretty decent. Stress levels are okay (if anything, I had a really stressful few months April / May / June of this year).
I started working out again after I got back and started taking protein powder. -- The same protein powder I was taking during the summer with no issues (and again my doc said he doesn't know of any correlation b/w protein powder and hair loss). Just over this past week I started taking another exercise supplement called Creatine -- I don't think this is related since I've been experiencing the hair fall for about 3-4 weeks, and I've only been taking Creatine for about 5 days.
The number of showers I've taken due to gym, etc over the past few weeks has gone up, though. Maybe up to 2 per day in the evenings, every second day (+1 shampoo in the morning = 3 shampoos every 2nd day). My doc recommended adding Rogaine to the mix for a few months to see if it'll help regain the loss. Continue taking Propecia/Proscar. And my hair dresser just told me about Mane and Tale Shampoo, which I went out and bought yesterday (yes, I'll stop shampooing so much and cut it down to 1x per day max).
-I may not have been getting enough protein in my diet in India
-My hair was really rough while I was away due to the water / sun / dust
-Doc mentioned weather change as a possible culprit
-Doc mentioned that this could just be a regular hair cycle, though I have my doubts on that due to how much is shedding all at once
Please let me know if you have any advice/questions/thoughts, as I'm quite worried.