Is it normal to see or hear things that really arnt there, while having sex?

while me and my boyfriend were having sex last night, we heard somebody talking and keys set on a table out in the kitchen. we were the only ones home, so of course we jumped up, got dressed and checked it out with nobody to be out there. this has happened to us three times now, were we both hear something, very clear as day, when nobody else is home or maybe even see something like a shadow walk by in the hallway. is it just in our mind, maybe the ecstasy from the sex playing tricks, or maybe something in the house?