Mark 14:32 - 42
ESV - 32 And they went to a place called Gethsemane. And he said to his disciples, "Sit here while I pray. 33 And he took with him Peter and James and John, and began to be greatly distressed and troubled.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
In short, I think he felt that the weight of the entire world was on His shoulders.
Jesus came to his disciples twice. I think He felt frustrated that His own disciples kept falling asleep on Him. Now, He's already come once -- to us, to the world-- but He will return in the Rapture for us. Will we be ready or sleeping? We are sleeping, spiritually, paying attention to our cell phones, video games, sports, etc. When we should be alert. Will He not be mad? Frustrated?