I don't really know what's happening? Help?

Okay, so I have been diagnosed with depression and social anxiety disorder. I've rather recently started struggling with extreme hypochondria, which is what brought me to this site to begin with earlier this year. Lately, though, I've been experiencing something that I can't quite identify and it's really disruptive to my life and overall functionality when it does happen. I'm not sure what it is, and the closest I can come up with is depersonalization or derealization.

Basically, and this always happens after a really bad depressive spell or a panic attack, I get this feeling that something is just "wrong." I suddenly feel really far away and like I'm not really there. I feel like I'm a machine and all of my actions are completely mechanical, so to speak. Now, these aren't delusions and I know that I'm not really a machine, but that's sort of what the feeling is like. It's scary because I feel like I'm not in control, and I'm just watching myself and responding to some outside command. I feel like I'm just doing things because that's what I'm supposed to do, and that's it. If I'm hungry, I'll make something to eat, but not because I want to. . . Because I'm supposed to. I feel like I'm not in control at these times. Even worse is the "visual" effect that it has on me. I'll look at my arms or my legs and they'll be smaller or longer than I remember them being. When I look in a mirror, I'll see something terrible and bloated and ugly (this can sometimes send me into another panic), and all I can think is, "That's not what I really look like. That isn't me." It's like my perception changes. . . And I don't understand it.

I would be more concerned about it if it didn't always happen after a really deep depression or panic attack (it never happens out of nowhere), and lasted for longer than a few hours. Luckily, it doesn't last long. It's just really startling and I don't really understand it. I was hoping that maybe someone else would know what was going on with me. Any ideas?