Why Don't You Get Blood Clots When You Sleep But Get It When You Sit For Long Hours?

Sitting for long periods can cause blood clots due to impeded flow of blood. Sitting without moving much can cause the blood to clot according to the effects of gravity. This doesn’t happen during sleep since we do move our bodies during our night’s sleep. In the ‘lying down’ or ‘sleeping’ position, the legs are more or less on the same horizontal plane as the heart. As a result, the blood does not have to work very hard to fight gravity to reach the lungs and heart. But the dynamics change while you’re sitting. While sitting, legs usually don't move much, and they are often angled. As such, the blood needs to fight gravity to flow upwards. The velocity of blood flow is impeded by the force of gravity. Thus sitting for long hours without moving much can potentially lead to blood clots in the body.