Beethoven was deaf. Everyone knows that. But he wasn't the only one. The most famous other composer was probably Bedrich Smetana, a Czech composer who is most famous for his work Ma Vlast (My Country). 
Smetana went deaf and because of that also went insane in his later years. Ma vlast is one of the most popular classical works that exist today.

Enrique Granados is probably one of the only famous composers to come out of Spain. During his lifetime he had a successful international carreer, and even played in the white house for president Wilson. On his return to Spain by boat (which he didn't like to do, for his grave fear of water), the boat was hit by a German torpedo and sank. Granados survived in a life boat, but jumped in the water to save his wife, and they both drowned. The part of the boat where Granados's cabin was located turned out to be perfectly unharmed by the torpedo and everyone in it survived the attack. 

Jean Baptiste Lully, the court composer of Louis XIV was leading an orchestra in honor of Louis's recovery from illness. During the performance he accidentally hit his own foot with the staff he was using to indicate the tempo. The wound became infected and had to be amputated. 
Lully refused, and consequently died.

Russian composer Dimitri Shostakovich was listening to "Tea for Two" with Nikolai Malko. Malko made a bet that Shostakovich couldn't re-orchestrated the piece from memory in under an hour. Shostakovich finished it in 45 minutes, winning the bet.