Think of it this way...
There is a big difference with a head getting purposely & forcefully smashed into something hard, compared to an accidental bump..
just not enough power or speed.

Mark and Jo*mar,

Thank you for your responses. The difference in force applied to purposeful vs. accidental head contacts makes sense. That is a helpful way of thinking about it, and I'll try to incorporate that into my thought-changing strategies when these bumps happen.

I am just having a hard time figuring out why I got a headache 5-10 seconds after hitting my head on the metal frame of my chair, and why that headache has been on/off since. I didn't get any immediate symptoms - no dizziness, no dazed/confused feeling, no visual disturbances, no balance problems, no nausea, no vomiting. I know those things tend to happen as indicators of a concussion, even if they're only present for a few seconds.

Maybe I just don't fully respect the power of anxiety.

Sincerely,
Squash

An upper neck trauma only required 4 or 5 Gs. A concussion required 60 to 90 Gs. Both cause headaches. Straining neck muscles and ligaments can cause headaches.

Ice your upper neck on and off for a few days.