This is probably normal behavior as swans will rest and even sleep in the water with their necks and heads tucked under their feathers on their back. You may have awakened him and he did not feel that you were a threat so he kept resting. If he was in a deep sleep, he probably did not believe that you or anything else was able to get near him and he was probably somewhat startled to see you so close, yet it did not quickly register. Think about when you are roused from a sound sleep. It takes a few minutes for you to assess the situation and get yourself together. So, as long as the swan was acting normal after your brief encounter, there is probably nothing wrong with the swan. The Regal Swan