Suggest Treatment For Frequent Fainting And Heavy Headedness

I have been experiencing fainting, was checked out at hospital with several tests being done including a stress test on the heart. Everything came back good. I still feel heavy headed at different times. I was told it may have to do with vasovagal syncope. I have ankylosing spondylitis and take enbrel. How can I stop the fainting? It happens so fast that I can't react to it in time.