I'm loosing time

I get to points where I loose hours at a time. I have no idea how to really describe what's it's like but I'll just have random periods of time where I know I did something i just have no idea what I did or what happened and I can't remember anything from that period of time no matter how hard I try. It feels like I just stopped existing for a while and it terrifies me. I have no idea what's making it happen or what I can do to stop it I just hate it and want it to end. All I know is it might be a part of my depression and it kills me knowing it stealing even more time away from me than I realize.