@riverflows, I think I found out the reason for indoor tomato leaves curling up and falling off. It is a classic case of over-watering.

Yes, there is always somebody on youtube who magically seems to have an answer for all of life's problems. As I understand, the small pot for indoor plants often means the roots cannot grow fast enough to keep up with the unrestricted growth of the foliage. The tomato will actually curl the leaves to block sunlight, and so it is okay to move the plant to a low-light area and stop watering until the soil dries out completely. This allows it to de-stress a bit.

New healthy growth has sprung out to replace the curled leaves. I noticed some tomato varieties are more susceptible to this problem than others. Beefsteak is the hardest one for me. Even in the summertime, I think it prefers a warmer, dryer climate than the rainy climate where I live, because it constantly gets stunted growth when stressed out after I water my beds.