A convulsion is a medical condition where the body muscles contract and relax rapidly and repeatedly, resulting in uncontrolled shaking. Because epileptic seizures typically include convulsions, the term convulsion is sometimes used as a synonym for seizure. However, not all epileptic seizures lead to convulsions, and not all convulsions are caused by epileptic seizures. Convulsions are also consistent with an electric shock and improper enriched air scuba diving. Non-epileptic convulsions have no relation with epilepsy, and are caused by non-epileptic seizures.

Convulsion is a common term generally describing uncontrollable muscle contractions. The term convulsion has been used interchangeably with the word "seizure". Seizures may cause a person to have convulsions, but this is not always the case. Convulsion is a type of seizure that involves bursts of electrical activity in the brain. Occasionally the reason for a convulsion is unfamiliar. A convulsion may be caused by illness, a reaction to a medication, or other medical conditions.

The word fit is sometimes used to mean a convulsion or epileptic seizure.

Source: Wikipedia

(G) Very specific problems