We all, at times, experience that feeling of dizziness and nearly blacking out when we arise too quickly. But if this has been happening on a regular basis since you began the Zoloft, you do need to see your doctor. What you may be experiencing is called orthostatic hypotension which is an excessive decrease in blood pressure when a person stands up, resulting in reduced blood flow to the brain and fainting. When a person stands up suddenly, gravity causes some blood to pool in the veins of the legs and lower body. The pooling slightly reduces the amount of blood that returns to the heart and the amount of blood pumped by the heart. As a result, blood pressure falls. The body quickly responds: the heart beats faster and the contractions are stronger. The blood vessels constrict, so their capacity is smaller. If these compensatory responses fail or are sluggish, orthostatic hypotension occurs. Most episodes of orthostatic hypotension result as a side effect of drugs. I will skip any further lecture on this subject except to say that SOME medications used for depression can trigger this. This is NOT a diagnose of what you're experiencing. But it IS why I think you should talk to your doctor. If this was not an issue BEFORE you began the Zoloft, then I believe, in my humble and non-medical opinion, that Zoloft could POSSIBLY be the cause. But ONLY your doctor can make that determination for sure.
I do urge you to see your doctor about this.
Peace
Greenlydia