Gentle yoga does help quite a bit when I practice it consistently, but it's subtle. I'll mostly notice that it hurts less just to lay there when I go to bed. BUT - overdoing does not help. If you are in that much pain, you need to listen to your body -- the video you used is a poor choice for you right now. Do not push yourself thinking "harder" yoga will lead to better results. The only way to get relief is to consistently practice and to
respect your limits.
I am extremely fond of yin yoga - mostly seated, very gentle. My very favorite find of all is a Gentle Yoga dvd by Zyrka Landjwit -- that's what I'd recommend.
I am a bit of a hypocrite because I fell off my daily yoga routine a couple months back, keep telling myself I'll get back to it and haven't. You'd think the extra pain would be all the motivation I'd need! Anyway, I hope you find a gentle form that works for you -- I really believe when done gently, it can be very helpful for fibro pain.