Red Superfly
You creepy little stalker
Yeah so until that day when we can speculate all we like.
I can't ebelieve people think that's what lightning does to skin though. Some people really need to have a look up a medical dictionary and have a read about skin and lightning burns. Better yet, go shock themselves and find out what happens.
I personally think it's Sidious true form being revealled, which has been suppressed for so long, but the lightning caused Palpatine to lose his ability to maintain his appearance.
I mean, old and wrinkly Emperor is his true form, but using a technique he was able to prolong his younger self. I think the lightning caused him to suddenly age as he lost his hold on his youth that he shouldn't have had in the first place. That's why he wasn't "deformed" as Darth Sidious - he had to keep it, or lose it completely. That would explain why he can't simply don the disguise afterwards.
Like in Lord Of The Rings when Bilbo gives up the ring of power, he ages really quickly. I think The Emperor had his own force rejunivation process, in order to slow down his aging process but the lightning caused him to simply drop the ball.