Many patients have an aura (sensory warning sign) preceding the seizure. This can include a visual, taste, smell, sensory, or other hallucination or dizziness.

• loss of consciousness or fainting, usually lasting between 30 seconds and five minutes
• general muscle contraction and rigidity (tonic posture), usually lasting 15 to 20 seconds
• violent rhythmic muscle contraction and relaxation (clonic movement), usually lasting for one to two minutes
• biting the cheek or tongue, clenched teeth or jaw
• incontinence (loss of urine or stool control)
• breathing difficulty
• stopped breathing or difficulty breathing during seizure
• blue skin color

• the person usually begins breathing normally when the seizure is over
• arousable but sleepy for one hour or longer
• loss of memory (amnesia) regarding events surrounding the seizure episode
• headache
• drowsiness
• confusion, temporary and mild
• may be weak for 24-48 hours following seizure (Todd's paralysis)

Diagnosis of a grand mal seizure is based on the symptoms and excluding other medical problems that can look like a seizure (such as heart arrythmia). A neuromuscular examination may or may not reveal neurologic deficits (decreases in brain functions) when the person is not actively having seizures.

An EEG may show characteristic changes and in some cases may show the focus (location of the cause of the seizure). An EEG can be normal in between seizures and a normal EEG does not rule out a seizure disorder.

Tests for the cause may include various blood tests (depending on the suspected cause), including:

• complete blood count
• blood chemistry, blood glucose
• liver function tests
• kidney function tests (BUN, creatinine, etc.)
• tests for infectious diseases (depending on the suspected cause)

• head CT or MRI scan
• lumbar puncture (spinal tap)