My Partner Who Has Had PD For 13 Years But

My partner who has had PD for 13 years but walks 2km/day suddenly felt giddy/dizzy & lost his balance & was unable to walk in a straight line but veered allover the place - this happened 3 days ago & he still can't walk properly & says he feels giddy/dizzy when he moves his head - he is ok when lying down & his general health is very good. The doctor gave him stemetil yesterday for dizziness (he has no vomiting or nausea & this is the first time he has been giddy)but it has made no difference & could interfere with his l-dopa. His BP was normal yesterday.
What do you suggest? Could it be neuritis which I just read about? Or an ear infection? Or a lack of good sleep as he gets up about 3 - 6 times a night to urinate so sleep is broken.
He is on kinson for PD, cartia for blood thinning, lipidil for cholesterol & pantoprazole for reflux. He had a stent put in in 1996.