Why does my left hand started shaking uncontrolably without a reason at all ?

Tremors: And shakes have many causes. Muscular, metabolic, neurological and sometimes just no cause can be found. The differential is huge and can be made worse or more apparent by a concurrent condition . You need to see your primary care provider to start the process of finding out what this involves.

Tremor: You may have a tremor. A neurologist can help you.