I think Jesus was frustrated because the Disciples didn't understand what He was saying. They couldn't see that Jesus was incredibly anxious and facing tremendous temptation. They failed to really listen to him, so they dozed off, not taking the time to really feel his pain. I wonder why they didn't get it? Jesus doesn't seem to be an overly dramatic person, so why didn't they see that something was wrong?
I think we spend too much time concerned about our own needs and too little really listening to people and trying to understand what they are going through. JM