I think everybody needs some time to be quiet even for no apparent reason..we just do..
Completely normal, I get those moments a lot. I end up sitting there trying to figure out what it could be. I'm not sure what brings it on I guess it's just a little phase that comes up now and then.
It's normal and natural.
I get that way too whenever I'm somewhere whether it'd be in church or school. We all go through the phaise and we need to figure out what's really bothering us. If something bothers you, I'd suggest seeing if you can talk to a close friend or someone you really look up too.
You just can't keep your emotions in for too long. Being quiet is normal.