We've all been there.
Someone rings the doorbell. You jump up to see who it is and — BAM! — you start to see stars. For a moment, you feel like you're losing your balance and about to black out.
The woozy feeling goes away quickly, but why did it happen in the first place?
As it turns out, it's because of the competition between a sudden drop in blood pressure and gravity. As you stand upright, the force of gravity pulls the blood out of your head and down toward your legs. For a moment, your brain doesn't have enough blood to supply the oxygen it needs to keep your orientation in check.
Once the circulatory system can catch up, everything is good again.
SciShow explains why that head rush hits you so hard when you stand up quickly — and whether or not it's something you should talk about with your doctor.
Check it out here:
Cover image: Shutterstock