Welcome in H.C.M.
I have gone through your query regarding heavyness at the back of your head, though you sustain injury over head.
As you said you had been investigated for so many things and still your heavyness in head is same, you have some problem in balancing also. here you are actually having sequely of head injury
which will recover with variable prognosis so you please remain in touch of your nurologist and physiotherapist.