Feeling of bed sinking in like someone sat on my bed but nobody is there?? Ghost?

The physical feeling of someone sitting on my bed with me Started about a year or so ago. Lately, this has been happening to me about once a week. It only happens when I am in the bed alone and now that my husband & I have separated (9 mo. ago), I am alone more often. Sometimes, I would just pull the covers over my head and move my feet around and try 2 convince myself it was me making the bed move & then just try to forget about it. Lately, I just stay really still because I have gotten so used 2 it & it still happens & I REALLY feel or know something is sitting on my bed w/me. The thought of spirits & ghosts REALLY scare the You Know What Out Of Me!! I know they exist but I just try 2 ignore the reality of it and not think about it. This weekend it happened & i stayed perfectly still & I know there was something that got on my bed with me. I even got brave enough to look & see if I could see the imprint of someone next to me!! What is it & has anyone experienced something like this?