How come when you stand on your head it starts to throb but when you stand on your feet they don't?

The heart is closest to the brain, so when we walk it takes longer for the blood to get to our legs (that's why we exercise) and when we stand on our head the blood basically gushes to the brain. Your brain is saying "Whoa, what the heck is that!" Actually, it's healthy to stand on your head (in a Yoga position) because at the beginning of time man never walked standing straight and if you consider how long in one day we are on our feet (not on our head) then you can see why some people have poor circulation. Yoga is an excellent exercise and very healthy for your body.

Our circulatory system evolved for our bodies in a standing position. It takes more pressure to pump blood into the brain because it is at a higher elevation than the heart than to the legs which are lower and can take advantage of gravity. If you are standing on your head, you are adding the effect of gravity to the pressure exerted by the heart.

IN ADDITION:

Its all about blood pressure. When you stand on your head or are inverted, you blood pressure is increased because of gravity. The same thing happens when you swim into the deep end of a pool. The extra pressure will cause you to be able to feel and hear your heart beat in your ears and sometimes feel it in your head, especially in the temporal artery. This is due to blood wanting to flow to the lowest point in the body.