When he was a adult

Before he graduated , Tchaikovsky worked as teaching assistant in a sing class. Several weeks before his graduation, Early in 1866 he began to work on his first symphony "Winter Daydreams". The symphonies were killing his sleep, and sleepless nights were killing his energy and paralyzing his creative power. In the middle of July, his doctor said, Tchaikovsky was even close to insanity.

http://pages.cs.wisc.edu/~boris/maha/music/tchaikovsky.html