My dad had his yesterday morning (Pfizer in case it's relevant). Was fine until the evening when he suddenly felt very very sick, vomited a lot, had diarrhoea, was sweating and hot, and couldn't move from the sofa. Woke up at 4am right as rain and took himself off to bed, has been absolutely fine since. My mother had the vacc at the same time and no illness at all. I suspect it was the vaccine (which he is delighted to have had and isn't complaining at all) but wondered if anyone else had come across this.