Just now seeing this and I hope you find out what's wrong poor little guy- it's so scary when we see them sick and it must be way worse to see them sick to the point of falling over
my heart goes out to you and I hope he's going to be ok. You got some good suggestions and I won't add to the guessing but I do hope you find out what's going on - that sounds like it sure came on suddenly... and sending prayers.....