Eels are pretty resilient. I wouldn't worry too much about him. Snowflakes and zebras are 2 of the hardiest fish I've ever owned. I had a zebra survive 2 tank moves, a tank crash, 2 outbreaks of white spot, a carpet surfing episode and being bullied (to the point he wouldn't leave his den, even for food) by a very nasty damsel. Plus he was a hitch hiker in a mates rock (he was only about 3"), so he went from the LFS to his house in a foam box with only wet newspaper for moisture, he wasn't actually submerged in water at that point. Sorry, I got a bit off topic there, but my point is how tough they can be.
If he starts losing weight id be concerned, but most morays can go a lot longer than you and me without eating.
Why are you treating him?