Is it normal to see things that aren't there? I've been seeing a person standing and staring at me in the distance with the corner of my eye but when I turn around no one is there. Is that normal because I'm starting to freak out a bit?

Humans have good peripheral vision.  You are hardwired to be sensitive to things around you, in case its a mountain lion.  I think I see things out of the corner of my eye all the time.  It is odd that you see this as a man and not just a "presence".  Also, that you think this person is staring.  It is worth a visit to a doctor.  Start with your family doctor.

Yeah many things cause this phenomenon. Lack of sleep to dehydration...even bad eyes. Its when they talk or look you in the eye that you have a problem

That's me watching...I see you.

It's not a big deal. As Moga Deet pointed out, the "corner of the eye" is just your peripheral vision. It's that part of the eye that relates to "night vision". You can see things that way that simply aren't there when you turn the full focus on them.

Here's an experiment you can try. On a clear day, go outdoors and look up at a tree with the blue sky as a background. Now, very gently, allow the tree to go out of focus. Just a little. What you're doing is trying to see it through your periphery. When you find the right change of focus you'll see a kind of khaki-green aura around the tree.

You're normal but you might have a lazy muscle in your eye if it's happening too much.

The human vision only sees a certain spectrum.

Animals see more than humans do.

If you could see all that is you would just sit in your

bedroom with the covers over your face and not want to come out.

Don't worry though, your safe. It could be a past relative just checking in. 

It is all alive, there is no death. Just a transition.

I believe that sometimes we see things that have no explanation, I also believe in angels so it could have been your guardian angel you saw.  Children and animals often see things we don't that's because their minds are open.

Don't be afraid of whatever it is, it's just watching over you.

Calm down :).... You seem like the type to worry a lot, which could be causing this. You need to relax, more people than you think have had a similar experience, most people are filled with worry... Your fear could be causing it... That's just my opinion. Your mind could be playing tricks on you...

(I believe in ghosts but I didn't want to give you that speech...)

It might just be YOU from the future trying to warn you not to worry about it.