What's wrong with my Pilea? 😭

I recently noticed a lot of the lower leaves dropping, turning lighter, and browning in some areas. When I bought my Pilea a month ago, the seller informed me that the lower leaves would really fall and that I shouldn't worry too much since there would be new growth anyway. But last week, 2 leaves with their stems fell from the trunk one after the other, and I don't think that's normal. Please help!

Additional info: My Pilea is an indoor plant and it doesn't really get much sunlight, though I keep the curtains open for it as much as I can. My window, though, is shaded so not much sunlight seeps through the covering. The other day, I saw multiple earthworms fall from the pot after watering.