It sounds like sympathetic shockloss is occuring especially being 17 days post-op. This is perfectly normal and I would not worry about it.
Had you stated that there was a definite sunburn as a result of the filtered UV rays, that would be different altogethor. Yet I did not read of any red burn nor inflamation or burn blisters of any kind. There is a fair amount of pain and acute tenderness associated with sunburn when the tissue is damaged.
It would be helpful to visibly see your scalp right now however trust me, you would know if your scalp was sunburned but it clearly does not sound that was the case. If you would have been outside say on a deck with your scalp exposed to "direct" UV rays, then you probably would have experienced a burn but thank goodness for those curtains and the fact that you were not "directly exposed" to the potentially harmful rays.
Now it never hurts to contact your surgeon, but my guess is that your doctor will concur with the opinion that you did not sustain a sunburn and that your grafts should be fine.
In approximately another 12 weeks, maybe earlier, you should begin to see the new growth. Wishing you the best my friend!