Why does my plant look like it's on the verge of death?

My mom gave me an ornamental pepper plant a few months ago. It was gorgeous – tiny red peppers about two inches long and green foliage in abundance. There are about 5 different plants and they were in a small pot.

In order to give them more room, I transplanted them. 4 into a larger pot and I left one in the small pot. I used potting soil. The two pots are in my office window, facing bright light but indirect sun. I have a window unit heater which I can turn on and off at whim, and I usually like it fairly warm.

I keep the soil reasonably moist but there have been times when it’s not always damp.

The leaves are curling and looking droopy. Two days ago I cut the dead peppers off and just left ¼ inch stumps. I thought that maybe the peppers were draining the plants of energy.

Any Jellies know about plants?