Generally, a real hallucination is usually pretty vivid and seems very real. Many people get that sensation that they are seeing something out the corner of their eye; that isn't particularly unusual, and being really anxious may just have you figuring the worst about that sensation.

I was having that same sensation of seeing things out of the corners of my eyes just a couple of nights ago. Kept thinking I was seeing maybe a bug crawling nearby, but I knew I had been without sleep for several days and that probably it was just the exhaustion from not sleeping. On the other hand, when I truly hallucinate I hear very distinct voices that actually speak or I see a person right in the same room. I was clearly in a psychosis at that time. Does the difference make sense?

You are stressed and depressed, and while hallucinations can happen under those circumstances, it is pretty unusual, and hallucinations are experienced as much more real.