It is common to feel dizzy after sudden change of the posture, like when standing up after sitting, and even after running (you have stop running and the blood goes in your legs, so, it result in feeling dizzy).
However, it is good to check the count of your red blood cells (anemia), heart work, and your blood sugar levels.

Best wishes!
Marija

yes i agree i suffered reccuring severe anemia for quite a while, and i got alot of the dizziness when standing, near fainting, real light headed, i also lost a hell of a lot of weight if this applies to you its a great possibility!! start eating more red meat, wholegrain bread and cereals, seeds, egg yolk, leafy green veg, potatoe skins and raisins, also supplements such as vitamin b12 and folic acid are great!!