You're in luck in that tropical hibiscus are hardy where you are.

These plants are pretty resilient, especially the garden variety kinds, which is what I bet you have. I've had them come back from being in the high 20's at night of almost a week, while getting no water and they were rootbound. They were covered with a tarp, but still - that's pretty extreme for a hibiscus!
It's hard to give advise without looking at the plant itself. The best thing for you to do is to take the plant to a nursery nearby. Not a big chain store, they don't have peopple there this time of year who know about plants. Since most nursery's in zone 10 areas sell tropical hibiscus, they'd be able to help you out.
Good luck!
Barb