Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
The causes of stroke are multiple and could include embolism from the heart or other areas (such as the aorta or other parts of the body), bleeds, atherosclerosis of the blood vessels, vasculitis (or inflammatory processes affecting the blood vessels of the brain), and others. The prevention of stroke typically depends on what are the risk factors a patient has. These may include aspirin, certain blood thinners, or cholesterol-lowering medications. If there is diabetes, control of that will hopefully improve the risk of stroke as well. Additionally, eating a healthy diet, exercising, etc. are recommended. There are risk factors that one cannot avoid such as a family history of stroke, prior stroke, aging, etc.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.