I have a beautiful indoor hibiscus. I re potted it in the Spring & it is thriving apart from a few leaves go yellow & I either take them of or they drop of. Could it be magnesium deficiency?
Check carefully for red spider mite - they're rather partial to indoor hibiscus, and produce these symptoms initially
If it's only a couple of leaves don't worry... has it had a stand outside? Often helps in Summer, certainly keeps the Red Spider at bay... :)