Thanks for posting your query at DoctorSpring.com
I have gone through your question in detail and I can understand what you are going through.
The hypnic jerks are common and normal for this age as well and may persist all through your life. They dont look like a seizure and you may continue taking your medicines. For some these jerks are mild while for some these are severe. But there is no requirement for treatment of this condition.
Regarding your second doubt that the back of your head feeling like exerted after blood rushing out through it, It may not be related to the jerks. Neither is it a sign of any congenital heart disease. Mostly it has something to do with the strain in your cervical vertebral area. It could be a spondylosis which may exacerbate when you physically exert. If its causing a lot of problem then you may get an MRi scan of the cervical vertebra done. This can help us in evaluating the healthiness of the vertebra.
Hope this helps,
In case if you have any further query, do let me know.
Dr. Srikanth Reddy