September 19, 2019

Why Do I Feel Lightheaded When I Stand Up?


So there you are, crouched low on the ground,
tying your shoe or inspecting some interesting bit of trash or sidewalk art or
spring flower… and everything’s cool until you stand up too fast. Then comes the headrush. Suddenly you’re all dizzy and feeling like
you might black out, and just as you think you’re gonna fall over, everything’s back
to normal, and you’re left wondering what the heck just happened? Well, probably your blood pressure dropped
is what happened. Your blood pressure will vary a little throughout
the day, like if you’re stressed or relaxing, running or sleeping, but in general it exists
within an average range. That said, individual’s normal ranges also
vary — for example, athletes typically have lower blood pressure than overweight smokers
— and what’s normal for you might be considered low or high for me. We’ve all heard how elevated blood pressure,
or hypertension, can be dangerous it puts extra strain on the heart, and can cause
arterial walls to leak or rupture — but low blood pressure, or hypotension, can also cause
problems. Like dizziness and fainting. Lots of conditions can lead to temporary or
chronic low pressure, like pregnancy, dehydration, anemia, or taking various medications. But there are a specific types of hypotension,
too, when it’s specifically associated with things like eating or nerve damage. When you stand up too fast and get that wobbly,
head-rushy sudden drop in blood pressure? Doctors call that orthostatic, or postural
hypotension. It happens because even though your blood
keeps circulating no matter what position you’re in, when you stand, gravity causes
some of the blood to collect in your legs. Your body is supposed to combat this by constricting
blood vessels and ramping up your heart rate — effectively increasing the pressure to
help keep enough of your blood flowing through important places like your brain. But sometimes when you jump up too quickly,
that sudden change in blood flow and drop in pressure can strike before your circulatory
system has a chance to recalibrate, and now you’re seeing stars and groping for balance
which is basically your desperate brain’s way of telling you it needs more oxygen. Usually it only takes a few seconds for the
adjusted blood pressure to kick in, but if that initial drop is too extreme, you could
actually faint. If you’re feeling faint all the time, especially
when you haven’t just stood up quickly … well, you might want to get that checked out. But
lots of people get head rushes now and then, and it isn’t a big deal. Still, if you’d rather avoid the dizziness,
just remember to take your time standing up the next time you tie your shoes. Thanks to patreon patron Alexa Singer for
asking this question, and thanks to all our patrons, who keep these answers coming. If
you’d like to submit a question to be answered, just go to patreon.com/scishow. And don’t
forget to go to youtube.com/scishow
and subscribe!

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