I'm not a medical doctor, of course, but I have noticed that people who are extremely active and have a strong drive to succeed sometimes seem especially susceptible to this puzzling problem. Perhaps this has been true of you.
Whatever the reason for your condition, I urge you to get the best medical advice you can. Seek out people who have also struggled with this problem; they can encourage you and help you face your situation realistically. The Bible says, "Encourage one another and build each other up" (1 Thessalonians 5:11).
The most important thing I can tell you, however, is that God has not abandoned you. He loves you, and He wants to help you deal with your discouragement. Instead of being frustrated because you can't do everything you once did, thank God for the degree of health you do have each day.
It's hard to be patient when illness or disability overtake us, particularly when we've been very active but patience is one of God's choicest gifts. The apostle Paul yearned to tell as many people as possible about Christ but sometimes he couldn't, because he was in prison for his faith. He wrote, "I have learned the secret of being content in any and every situation" (Philippians 4:12). May this be your experience, as you commit your situation to Christ and ask Him not only for healing but also for the peace and joy that come only from trusting Him every day.