Anyway, what illness are you talking about here? Boredom? Got stuck in a place where the project sucked the life and general interest out of you? OCD? Depression? Anxiety?
UPDATE: Got good answers about what can cause these symptoms.
If you want to leave IT then try to find jobs that are still challenging your creativity, but don't need huge amount of concentration in the same time. Like becoming a carpenter, professional gardener, etc...
These still make you use your creative side, but rely on more physical work then intellectual.