Everyone gets worn out/burned out/discouraged/afraid--even great men of God. How many times have you said, "I've had enough! I can't take it anymore!" It's a common feeling--having had enough--wanting to end the pain. But God promises that he has a purpose for us and that he will fulfill it. (Psalm 138:8) Just because you are discouraged does not mean that you are not a Christian. It may mean that you are alone in the wilderness. It may mean that you are tired and hungry. It may mean that you need to hear a word from the Lord--which is what happens to Elijah later in the story.
When you are worn out/burned out/tired of running you need to take care of your physical needs. You need rest. You need food. It sounds simple, but it's the way God made us. If you are going through a difficult season of life, take care of yourself. Sleep. Eat. If you don't, the journey ahead will be too much for you.
When you are depressed, things look worse than they really are. In verse 14 Elijah tells God that he is the only prophet of God left. "And now they are trying to kill me too." God assures him that he has preserved a remnant of 7,000 others in Israel who have never bowed down to Baal. Elijah needed to see the situation from God's perspective.
So if today you are saying, "I've had enough!" Stop. Rest. Eat. Look at your situation from God's perspective. Listen for His voice. He will strengthen you for the journey ahead.
So do not fear, for I am with you; do not be dismayed, for I am your God. I will strengthen you and help you; I will uphold you with my righteous right hand. (Isaiah 41:10)