What Causes Seizures Episodes With Parkinson's Disease?

Hello! My husband, Phil, has Parkinsons and is taking stalevo 150 four times a day, Namenda 10 mg 2 times a day, celexa 10 mg one dose/day, and uses the Exelon Patch and Neupro patches. Yesterday we were sitting poolside for 90 minutes, and while not in direct sun, he had a 'seizure' type episode (ie could not walk, froze) and went to his knees. After sitting for 5 minutes or so, he was able to get up and get into air conditioning. Would the patch(s) sun combination cause that? And, would his concern over drinking too much liquid due to incontinence contribute as well? THANKS.