I'd go with him. Surely if you are feeling crap, it would be good to have someone else look after him for an hour or two? I had tonsillitis when DS started his settling in sessions - I felt vile, but sitting in the nursery kitchen or out on their balcony with a cup of tea and some water was far more preferable to managing a 1 year old!
But am I not risking spreading it round all the other little ones? And staff?
He goes to a crèche no problem so I think he may not need me there for long, but apparently I have many forms to fill in and need to get to know the key worker so I'm guessing I will be there for a good while regardless of how he copes?