What Causes Frequent Black Outs?

Hi,I am 31 years old (male).from last 9 days whenever i get from sleep i get a black our for 4 -5 seconds and the same thing happens when I am leaning back on chair and suddenly come forward and gets black out and after 5 seconds it normal again.I have visited a numerologist doctor he gave me vertin 16 .Please advice what is the cause of these black outs .