Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Your physician is going to be the resource for advice since I am not privy to the details of your clinical history, the dose of medication you re taking, other medications you may be taking, or any laboratory or other data about you to know exactly the reason for your dizziness and how best to fix the problem. However, this is a common problem with Sinemet. Often, it IS question of BP, except not as you perceive it. Simply taking the blood pressure doesn t tell the whole story. As a side effect sinemet can cause something called ORTHOSTATIC HYPOTENSION to occur. This will cause blood pressure to drastically drop whenever standing from either a lying or seated position. There could be also be a DRUG TO DRUG interaction going on causing this problem (though less likely since you re only reporting something wrong upon standing). Again, I emphasize the utility in speaking with your doctor to say what they say first before making any changes to your regimen or deciding on not taking the medication. Hope I have answered your query. Let me know if I can assist you further.