Hi,
I had a cat that was born with a severe heart defect that went through a stage like this, and we were told that it was epileptic fits. Does he go to eat once they have finished? as this was a typical thing to happen once she had recovered, and people do the same, as a fit stimulates the appetite. If it is fits, then don't talk to him when it is happening, turn off any lights, the T.V., any noise, and therefore reduce any thing which will act as a stimulus for the duration of the fit. My girls' used to last up to five minutes, and she would literally drop off the table etc to the floor, and be unable to get up. She went on to be put on a drug from the vets, and these seemed to help along with doing the above. She finally suddenly stopped having them after about 18 months, which was a huge relief as they were awful and distressing for us all.
Good luck
Plessy