This question is inspired by the recent gender identity topic.
If you woke up tomorrow and found that during the night you had magically been transformed into a fully functional member of the opposite sex, how would you react?
Everyone still remembers who you were but when you tell them what happened they just shrug and say "it happens" and they accept it (part of the magic). Government departments will change your ID for you becuase "it happens", your bank will change your details etc. so there's no problems with your identity being lost, just how you deal with the physical change.
*Edit*
New information added in response to a couple of comments.
With apologies to those who have already voted if this new info causes you to want to change your vote.
Your sexual preference won't change, if you liked girls before, you still do.
You won't be ugly but you won't be gorgeous either. You'll be somewhere on the better than average looking scale of the spectrum.
The magic isn't going to wear off so unless the magical entity that did this to you responds to your initial begging, the only way back is sex reassignment surgery.
Your thought processes will remain the same but you will be at the mercy of your new hormones. So the newly created women are going to be aggressive and irrational once a month, the new men are going to be like that all the time. :)