9 year old son complains of being dizzy and weak and can't sit up straight. usually after he does some physical activity. says his head is gonna burst?

Get him checked out: This could be nothing--age appropriate/typical dizziness (the so called head rush) when someone sits up too fast. However, i'd run that story--w/ a lot more important q and a. By your kid's doc esp if getting worse!

Check it out: Weakness, dizziness, headache associated w/ activity always needs checking out. Increasing activity raises heart rate &blood pressure(bp)so dizziness shouldn't happen. But shortly after exercise, it's normal for it to fall quickly. If BP is naturally low to start with, it gets even lower then. If you sit then stand again, BP can take a few seconds to catch up & voila! head rush! but see md 2B sure.