I'm a 22 year old female. I have been diagnosed and on meds for depression for over 5 years and honestly the past 9 months (approximately) have been the most stable ones in a veeeery long time. I've felt numb as any depressed person would but the suicidal thoughts have almost completely ceased to exist and I'm working on my goals and stuff. 

Good things there.

But I have been having something weird happen to me the last 2 weeks or so. I've been seeing things that aren't there (for example, I'm doing something and see a fluffy blob on the floor and I go out to get it or call it thinking it is my cat, only to realize there's nothing there, or I think someone entered the store I work at and go get them only to find out no one did).
Sometimes I even get "scares" thinking something is coming at me and I move to avoid it (think, for example, as how you would avoid a tennis ball someone threw at you) but then again it's nothing.

Today I had the most "real" feeling experience though. I was out on a museum with my sister, we were sitting on the ground and while there wasn't complete silence because I could hear the people around us walking, it was all very moderate volume. Then I started hearing my sister calling my name very close to me, so I look at her but she was looking at the paintings. Then, again, but this time I tell her "yeah?" and she says "what? I didn't say anything". Then, once again, I swear I could hear her say something (this time I couldn't get what was it) and I tell her "I know you're talking to me so just tell me what is it or shut up" in a playful manner because I really did think she was messing with me, but she replied back in a slightly annoyed tone that she wasn't talking to me and haven't had said anything.
I kept hearing it but stopped asking her about it.

I haven't changed my meds in a very long time but these new symptoms are something I've never experienced before. Does anyone else with depression experience something similar to this or should I be more concerned about it being something else?