The shadow of?

My wife and I had recently moved into an apartment. My wife had gone shopping with a friend, and I decided to take a nap on the coouch. After about fifeteen minutes I had dosed off. Soon to feel like I was being choked. I opened my eyes, and no one was there. I still felt like someone was choking me. I sat up and the sensation dissapeared. About a week later Ii was putting together a desk, and saw a shadow behind me. I quickly turned around, and again, no one was there.That was the las I saw or felt anything in that apartment.