Generalized Tonic-Clonic Seizures

There are two phases to grand mal seizures :

Tonic phase : The person loses consciousness, and their muscles immediately contract, causing them to collapse. This stage typically lasts 10 to 20 seconds.
Clonic phase : The muscles begin to contract rhythmically, flexing and relaxing in turn. Typically, convulsions last no longer than one to two minutes.
Some persons who experience grand mal seizures show the following signs and symptoms, however not everyone does :

Screaming : A few people may scream at the start of a seizure.
The inability to control one's bowels and bladder may occur during or after a seizure.
Unresponsiveness following convulsions : After a convulsion has ended, you may remain unconscious for a few minutes.
Confusion : After a grand mal seizure, there is frequently a period of confusion. Postictal confusion is the name for this situation.
Fatigue : Following a grand mal seizure, sleepiness is usual.
Severe headache : Grand mal seizures can leave patients with severe headaches.
On rare occasions, having a seizure might result in harmful situations for you or other people. You could be at danger of :

Falling
Drowning
Car crashes
Obstetrical complications
Emotional difficulties
If you have any of these symptoms visit a Neurologist to be diagnosed and treated properly

Seizures disturb the normal electrical activity of the brain and cause a large number of nerve cells to fire at once. What specifically triggers the alterations is still a mystery. Grand mal seizures, however, can occasionally be brought on by undiagnosed medical conditions,such as :

Injury or infection
Infections like encephalitis or meningitis, or a history of such infections
Traumatic Head Injuries
Injury brought on by a previous oxygen deficiency.
Stroke
Congenital or developmental abnormalities
Brain cancers
Genetic disorders
Abnormal blood vessels in the brain
Metabolic disturbances
Extremely low blood levels of sodium, calcium, magnesium, or glucose
Withdrawal syndromes
Addiction to or abstinence from substances, especially alcohol
Risk factors of Grand mal seizures include :

A history of seizure problems in the family
Any damage to the brain brought on by a stroke, a traumatic brain injury, or another condition.
Being sleep deprived.
Health issues that alter the electrolyte balance
Using illicit drugs
Heavy drinking

The tests listed below can help in Generalized Tonic-Clonic Seizures diagnosis and evaluation :

Electroencephalography (EEG) to assist in separating seizure disorders from other diseases.
Brain scans such as MRI to check the brain for any scarred areas.
Neurological exam
Blood tests to look for indications of genetic disorders, infections, blood sugar levels, or electrolyte problems.
Lumbar puncture
Computerized tomography (CT) scan to show any brain anomalies, such as tumors, hemorrhage, or cysts, which could be causing your seizures.
Positron emission tomography (PET) to assist in identifying disorders by making active brain regions visible.
Single-photon emission computerized tomography (SPECT) to produce a thorough 3-D image of the blood flow activity that takes place during a seizure in your brain.

Anti-seizures medication :

Carbamazepine
Phenytoin
Valproic acid
Oxcarbazepine
Lamotrigine
Gabapentin
Topiramate
Phenobarbital
Zonisamide
Surgery and other therapies :

Surgery
Vagus nerve stimulation
Responsive neurostimulation
Deep brain stimulation
Dietary therapy
Lifestyle modifications :

Wearing a medical alert bracelet
Taking your medications as prescribed
Getting adequate sleep