Air.

I've noticed the past few years, that sometimes I cannot breathe very well. I might go a few minutes without breathing, then my chest feels heavy and I take a deep breath in. Deep enough to overcome some threshold I feel needs to be met. If I don't reach it the first time I have to consciously do it again. These feelings last hours, or even all day. All day of not breathing, then taking a huge breath in. It was like that at school all day yesterday, and it started again when I got home a few hours ago. It feels weird, not breathing, and it is really tiring. It makes my eyes and head hurt. I feel the stale air sinking in my lungs waiting to be expelled, like WTF is the hold up? I wonder why I do this sometimes. Dunno if it is my problem, but the only thing I found online was it is an anxiety thing. That having periods of feeling like you can't get enough of a breath, or feel like you aren't breathing is because of a panic thing. Might be true. Dunno.

All I know is that when it happens, I am aware of it and try to control my breathing for a while. It gets old.