A stroke is the sudden death of a portion of the brain cells due to lack of oxygen. A stroke occurs when blood flow to the brain is impaired resulting in abnormal brain function. Brain blood flow can be impaired by blockage or rupture of an artery to the brain. Blockage of an artery of the brain by a clot (thrombosis), leading to deprivation of blood and oxygen, can cause a stroke. The most common symptom is weakness or paralysis of either side of the body.There may be partial or complete loss of voluntary movement of and/or sensation in a leg and/or arm. A stroke can result in speech problems and weak facial muscles which can cause drooling. Numbness or tingling is very common. A stroke can cause difficulty in breathing and even unconsciousness.