What Causes Fainting Along With Severe Fatigue And Confusion?

Thanks, My 28 yr old son has recently fainted once, and felt like fainting twice more. After these episodes he feels extremely tired, confused thinking. He lost a considerable amount of weight in late November and into Dec 2017. He has low platelet counts for 10 years at least. About 5 years ago one hematologist decided that is just how his blood is. But now with the weight loss and fainting, we wonder. He has had many blood tests that are normal except for the low platelet count. He has another hematologist appt on 2/20. But it seems like he is repeating what has already been done. I m concerned something else needs to be considered or tried. I d like to know your thoughts. thanks, D