This can be caused by bppv benign paroximal positional vertigo.

It can be checked by a procedure of moving your head when lying on your back on a bed. Then the Epley procedure id used to get rid of it.

You can do your own research and get a friend to do the procedure or your doctor should be able to do it.

I had this and ended up fixing it myself, and got the nhs to perform it as well as it can take a few goes.

If you've had concussion and banged your head you may have dislodged crystals that are formed on stems in the ear. If these are dislodged they can end up going down vestibular canals and affecting the flow of liquid that determines your balance. This disturbance confuses the brain which then sends a vertigo signal because it can't determine which way you are moving because the signals are different between balance systems from both ears.

Thanks. I wondered about BPPV myself as the symptoms seem to fit (though I haven't banged my head). Otherwise it is more serious--presumably involving something to do with my PN but I'm not sure what.