bizarre

This morning at 4AM, someone knocked several times on my door.  Not my main level door, but my bedroom (second story) door.

I don't know if they tried the main level first and I didnt hear it, or what.

Anyway..It startled me and I quietly crept downstairs to look through my peephole, hoping to catch a glimpse of my drunken 20 something neighbors, but I only saw the man across from me go into his apartment.

This act had me paranoid all day...wondering why someone would try to see if I was awake at 4AM.

Whats scarier is that I automatically assume danger.  Why is that?  Something has harmless as knocking on my door, and all the sudden I'm desperate enough to ask Thomas to spend the night.  I'm convinced I'm going to get murdered....because of an action as simple as a knock on the door.

Can anyone explain this?

Things I know-  it couldn't have been someone I know.  They would have called, or knocked longer. 
 My neighbor went into his apartment moments after I went downstairs, but didnt come from the direction that would make the most sense, if he had knocked my upstairs door.


I am skerred.  and I can't really explain why.