Yay Dude! Carpe tickle!
You'd have regretted it for the rest of your life if you hadn't taken the chance. Now screw up your courage and try it while she's awake. Maybe she'll like it, maybe she'll think it's fun, maybe you'll have a tickle-friend for the rest of your life!
Then again, maybe she'll tell you to stop, and she doesn't enjoy it. In that case you stop. You haven't lost a thing, but you're not left wondering "what if" for the next fifty years.