I just want to get opinions first

I'll be walking somewhere with a friend or two and i'm always kind of quiet. Once i was walking into my friends house for the first time, she was a new friend. We were already good friends though and the moment i reached the top of the steps i stopped and froze. I felt horrible, like there was something after me, like i was in pain (But i wasn't, you know?), and i felt betrayed. My friend asked what was wrong and i said nothing and the day went as usual but everytime i go there, it's an overwhelming feeling.

Another time i was at my other friend's house and she started to talk about her grandpa. It was a normal conversation, while i looked over my shoulder because of the previous feelings which were mentioned, but suddenly i felt like i was alone and that every moment took more then half my strength. I continued to talk to my friend and i asked. "Is your grandpa okay?" She looked at me funny and asked "Why?" And i shrugged. "I just worry i guess."
A week or so later, her grandpa died.

I've had other times like this and i don't know why. Is it a phase in developing, or is a something psychological?

I want to know if i'm going crazy, or that it's part of normal psychological development.