I went through a similar fear when I was a teenager. I recall very vivid dreams (or were they?) of alien abductions or seeing ufos in the sky from my bedroom window. I have had dreams and woken up with strange markings and nosebleeds. I had an irrational fear of taking a shower and pulling back the curtain with an alien just standing there. I swear something must have happened in my childhood. I have no other irrational fears like this. :/