scottu

Over winter and inside your plants have less optimum conditions and have to adjust. Pics would help to give best advice on yours in particular. If you had them in the ground outside or even in pots, they have less light, temps are off, humidity etc. Unless you have almost perfect conditions inside, it's dormant season. They will lose leaves, they don't need as many now.
Just keeping them alive is the main goal, that and Picking the right ones for your ambitions and timing their growth so they are where you want in april or so.
SDC are always losing the bottom leaves over winter, look closely at the under and overside of leaves for the tiny spider mites, they are easy to miss till it's bad, try turning the lights off and shining a small strong flashlight longways along the midrib.
if you see tiny dots in a web you have them and its time to get some neem oil or azamax, follow directions, easy fix with a few doses.
Good luck

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Viva La Banana