welcome to HealthcareMagic
If these symptoms are since 3 months and started after injury
to head it needs to be considered as really important & get investigated.If your cousin is getting paralysed please consult a Neurophysician first if all investigations & report say that there is no neurological damage then nothing to worry.As for depression
it is seen in some cases that post injury to head there occur few changes in personality in some people ;also memory can get affected.If it is not neurological then consult a Psychiatrist
who will help your cousin by counselling
or if required he can prescribe some medicines for this problem.
Wish him a speedy recovery.