Some snakes just like to soak, and sometimes soaking can be a sign that he could have mites. Did he do any soaking before today, or is this the first time?

When he gets out of the water, you need to check the bowl for tiny black dots a tad larger than the period at the end of this sentence.

If you can't find any mites, you might just have a soaker on your hands. Is his water bowl over the heat source?