So here's the deal. . .I had one of the PA's in my surgeon's office explain to me why the hair loss. She said that when you do something as drastic as removed 85% of you stomach your body thinks that it is dying because a major organ has been compromised. So it starts sending all of it's energy to all of the major organs in an effort to save itself. Thereby not having any energy left for any of the peripherals - hair, nails etc. So your hair follicles actually die immediately after surgery but it takes 3 months for them to work their way out of your scalp. That's why you start experiencing hair loss at about 3 months out. LeslieH is correct that it normally lasts for about 3 months and then will slowly subside.
My hair was very fine to begin with. I wore it in an A-line bob and colored it - both bleach and color, just to have some texture to it so that it appeared thicker. Once my hair started coming out at 3 months I started to freak out and went out and bought 5 wigs - very cool wigs, I might add - you'd be amazed at what's out there. I just could never bring myself to wear one. So I ended up cutting my hair really short (which I thought I would NEVER do) still color and bleach and everyone loves it, including me! When I was 60 pounds heavier I would have never been able to get away with a cut like this because my face was way too fat, but now it looks ok.
This surgery will change your life. No doubt. It is such an amazing transformation you will be in awe. I, too, freaked out about the hair loss and I'm not going to tell you that I didn't have some incredibly emotional times over it, but the weight loss and the new life is SO worth it. It doesn't fall out completely and for many of the gals that have gone from really thick hair to normal hair or even thin hair, when I see them, they still look fabulous - one would never notice the hair loss. Sleeve4me uses those clip in extensions and you would never know it's not her own hair - looks incredible. For me, I just went really short and honestly, don't think I will ever grow my hair long (er) again!