Hmm... to hopefully spark things off, we'll answer the thought experiment.

[quote="RPGN"]How would your character react and do if they were to wake up one morning as the opposite sex with no given explanation? How would a situation like that play out?[/quote]
Well, the character would have a -5 due to confusion, that's for sure. It would probably cause all sorts of havoc, probably somewhat different depending on what gender change it was. We imagine our characters would have all sorts of confusion with having new hormones flowing through the body, as well as a few different organ setups. It would probably not be pleasant. One factor we'd think as affecting the confusion is whether the sense of own gender is affected. If (S)he thought of self as the new gender in mind, it would be less confusing, but if say, a he still thought of it as himself, rather than herself, it would be harder to accept.

Then there is the issue of how the body is shaped and how to clothe it. Males-turned-female would probably have a bit of trouble adjusting to feminine clothes. This would of course be affected by era. In a medieval society, it would be very different from a modern/futuristic era.
Another important factor to consider is body size/weight and balance. If the male-turned-female has the type of boobs that many of the less mature males salivate over (i.e. huge ones, if you were in doubt about reference), the character would have a lot of balance issues. It doesn't take a genius to figure out that huge boobs are heavy.

We could probably go on quite a lot further, but we think we covered the basics of our characters' probable reactions on a general basis.