D.P.
D.,
Energy remains after the people, events, circumstances are long gone. That's just a fact. Some people pick up on it (sense it) more than others. My mother's house has a 50+ year history of paranormal activity. We've all experienced it. Some to more degree than others. Nothing scary or harmful. It's not something to be afraid of.
Try to find a group of like-experienced people in your area and learn about it. Often fear is the result when something is not understood. You're not crazy, you're just sensitive to/aware of the energy.
Good luck!