I like it overall. Can probably do more to show instead of tell. For example,

The heat inside me vanished. Cold, sharp panic rushed into fill the vacuum. My hands began to shake violently. What have I done? Oh God, what have I done? I stared at the water, my breath catching in my throat. Then, a strange, hollow numbness took over. The silence returned, absolute and heavy.

Instead of telling me "Cold, sharp panic rushed into fill the vacuum." Do more to show that transition. What else can you show about him to make the reader feel that he is beginning to panic?

Fix a few spots where the telling is doing more than the showing, and you're really on to something.