Well, this is...telling. Of pretty much all the answers, most come down to "masturbate" or "ogle myself." Of the one female-to-male that I've run across so far...
Pee standing up. Then walk around outside without a shirt on and feel giddy about doing so. You lucky buggers.
I'm pretty sure this says something, but I'm really not sure what.
Anyhoo, answer to OP: I'd probably wake-up enough to realize the change halfway through the shower, then spend the rest of the morning trying to figure out the rest of the rules that the universe is working under.
First up, driver's license. If the picture is still me as a guy, then my day is probably going to be spent convincing people that I'm me. Or, once my dad's out of the way, I can probably get by pretending to be my sister, or just a third sibling I never told anyone about. Playing most details of my life close to the chest has some advantages, as it turns out.
If the license picture is the 'new' me, then my job is that much easier. Now I just need to figure out why exactly I've become my own distaff counterpart. Oh, and then check in on my friends/Facebook to see how my life is different following the retroactive changes switching genders brought.