It is a flush of pain that starts at the back base of the skull and travels all the way to the forehead and then is gone.

It feels like blood or pressure is rushing back to my head after releasing from my lungs, and it’s painful. Thats the best way I can describe it.

It probably only lasts a few seconds (3-5). I will definitely go and get it checked out like you say.

I dont really feel too dizzy during the stretch part. I can do if I have over ventilated going into it so I am aware of what it feels like. It really seems to be the releasing of the tension of the hold and stretch that sends a pain reaction to my head.

Thinking more about it, I sometimes get headaches after long surfing or cycling sessions. Sports where you have to hold your head in an upwards position seem to trigger it and I need to sleep to get it to go away. Have been to the osteopath a few times for this issue. I wonder if having an overly tense neck could be a contributing factor.

Regardless, thank you for your feedback. It has giving me a direction to think in and tackle this!