What Causes Recurring Dizziness And Impaired Balance While On Radiation Therapy?

When I am driving for a prolonged time, say 45 minutes, once I get up from the vehicle I will suffer acute dizziness. Sometimes my legs will wobble and I have to lean on something. Even my arms will sometimes feel like they have no strength. If I simply lean forward so my head is lowered, the symptoms goes away within 20 seconds. This usually happens after participating in a hockey game. However it has happened after no physical activity. The consumption of a couple of beers will make the likelihood of this occurring more likely. However it also occurs without alcohol involved. I also have ED issues for the past 10 years – after undergoing Chemo and radiation for cancer– not sure if this even related. I am overweight – 6’1” – 235 lbs. but play hockey 3 time a week. It usually only occurs, as mentioned before when I have been driving for at least 30 minutes. While driving, no symptoms but I know that once I get up I will get dizzy.