Why Ethan is so sleepy?

It's almost 4 hours since the last feeding, however Ethan is still sleeping deeply.
We are worring about you, Ethan. Wake up for a sweet meal!

This is the first time Ethan sleeps for so long. Finally, we waked him up and he had 25-30ml mommy's milk. That's a relief at the end. We were so happy to see him eating.