Yes, it's normal. Not desirable, but normal.

The reason: The decreased light level indoors (compared to outdoors) means that the leaves will drop and be replaced by leaves adapted to low light conditions.

Then, later on, when the plant is returned outdoors, the process will repeat. This time the low-light leaves will drop and high-light leaves will form.

The ideal would be to keep the plant outdoors but bring it indoors only if it would freeze.

But, because I don't have a clue where you live, that suggestion may be irrational.

I experienced the same thing with my hibiscus. In addition, it developed sticky substance covering the leaves and tiny bug-like whitish in color after I brought in this October. The sticky substance and the white bug (if it was) disappeared after I sprayed it with organic insect killing soap. It looks very healthy now.

I have a tropical hibuscus tree also that I bought this summer and brought inside. It is not practical for me to put this out during the day, and bring it in only when it gets cold. We live in zone 7 VA and just had our first early snowfall.

My hibiscus is dropping leaves and yellowing, etc., but what I want to know is do I stop watering it as much? During the summer, I used to water everday because the tree couldn't get enough water. Now I water liberally twice a week or so. Is that okay?