Sandra,

The problem you describe is fairly common after chemo and radiation. Orthostatic hypotension as Mr "T" points out is the clinical diagnosis. Check the bp in your ankles immediately after it happens. You should see elevated bp with arm bp normal or maybe low. The problem is really from nerve damage created by chemo and much more so by radiation. Dehydration, electrolyte imbalance, especially potassium, exacerbates it. Checking bp in each arm, ankles can also help identify carotid issues from surgery early on and the carotid should be periodically checked.

With all the nerves in the neck it is difficult for the signals to get past the neck both coming and going. The nerve involved is the longest in the body and has two main branches, one down the left and one down the right. The right side senses the needed change in bp and heart rate then adjusts things as you get up and walk

If the dizziness happens almost as soon as you stand it is more likely a dehydration problem. Of it usually happens between 7-12 steps it is a lag in nerve impulses from radiation, chemo or any combination.

The easiest check for dehydration is taking bp standing and sitting. If it is much lower standing there is a high likelihood dehydration is the cause.

Another contributor to the problem is excess calcium and calcifications of veins. This is pretty common too after treatment. The natural process of cellular destruction/trauma is using more potassium while throwing off calcium. High serum calcium needs to be addressed as calcium plaque buildup has a lot of problems. It is often ignored unless over 11 with abnormal parathyroid hormone levels as the parathyroid glands regulate calcium levels.