We don't grow hibiscus but many plants will drop their leaves and even droop when you move them inside. Try not to put it close to a heat source, water less frequently and put it where it gets light but not direct sunshine. The plant is probably just getting used to its new growing conditions. It may have gone dormant. When it starts to leaf again, it might need a light pruning. Hope this helps!
Gjones has some good advice. The habiscus needs full sun. Place in a south window. Will stand down to 50 degrees in winter. Do not fert until growing and use diluted to half or less and only once a month. Also needs extra magnesium, 1 Tablespoon to 1 gallon in between fert.Turn only 1/4 turn at a time. Allow to dry between waterings @bugslife