Dear Sir, Hi & Welcome. Incomplete history like other prescribed medications or any other medical illness? You seem to have developed the first dose effect as a result of low blood pressure due to change in posture apparently caused by Tamsulosin. Tamsulosin is an alpha blocker commonly prescribed in the treatment of benign prostate enlargement to improve the urination and other symptoms. It is known to cause dizziness, fainting, blurring of the vision, headache, vomiting, diarrhea on sudden change in posture etc. These side effects are usually encountered when you first start taking it or when you start taking it again. Your blood pressure will need to be checked often. Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Get up slowly and steady yourself to prevent a fall. Avoid standing for long periods of time or becoming overheated during exercise and in hot weather. Consult your treating physician if the symptoms recur. Hope this will help you.