The injured brain often struggles to maintain proper pressure in the head. You symptoms when you get up from being bent down are not uncommon. It can take quite a while for the brain to recover this ability to maintain proper pressure.

Chiropractic can be helpful. Many find that the 'twist the head and pop the neck' adjustments are too aggressive. You should be icing your neck after a neck adjustment.

It is surprising that you can work out without head aches yet you struggle to get up from bending over. It is good that you can work out. Just don't push it to cause a head ache or other symptoms.