Dizzy spells have always been a part of my PD. iIt's called postural hypotension, and it kicks in when I stand up from a sitting or lying position. It is exacerbated by the hot weather, and by exercise, eg brisk walking. A blood pressure monitor at home is a good idea - my BP can go as low as 60/45, The medication I take for it is Fludrocortisone, Pyridostigmine, lots of fluids and a little extra salt in the diet. The main risks are falling during a dizzy spell, or the BP going too HIGH when lying in the fully recumbent position.
I suggest you talk to your GP/consultant about it.