Hairloss on leftside only. Test be done.

There has been hair loss on only front-left side of my head from last 3-4 years. Around 2-3 inch area of left side of my head has very thin hair which looks kind of odd. Tried medicine, oils,shampoos as consulted by various doctors but it doesn't have any improvement. This all started week after i did headstands for a week. i doubt if any small vein in that area got blocked during headstand due to external pressure as the hair loss is located only in that part of head and its not spreading in any other area of my head at all. I would like to know if this is possible and it will be great if there can be test for this to be sure. kindly suggest if there is any kind of test that can be done to check vein blockage within that area and where can this test be done. Thanks.