My6yr old spaniel started thrashing around & fell over. he wasn't able to stand for about 10 mins. any info?

he's in good health (or so i thought) and was sleeping on the kitchen floor cuz its cooler there. i heard a thrashing and went to check on him, and he was trying to stand and kept falling over. i checked to see if his paw was caught in his collar (which has happened in the past) but it wasn't. i sat down next to him and pet him, trying to calm him down to see if i could find the source of the problem. (thinking maybe he stepped on something or anything like that) but he hadn't. he sat up and quickly wobbled over onto his back, he was shaking (which he never does) then all of a sudden he got up and ran away as if nothing had happened, but was still shaken up for a few minutes after that. i love my wub very much, and YES i'm going to take him to the vet tomorrow after work. i just wondered if anyone has any info on this happening to their pets before that may prove useful to provide to the vet.