Seizures:

A seizure is caused by a sudden burst of abnormal electrical activity in the brain. It can occur without warning or be preceded by an "aura"—a strange sensation like a smell, taste, or visual disturbance. During the episode, the person may lose consciousness
 and experience tonic-clonic movements (stiffening followed by jerking of limbs), eye-rolling, frothing at the mouth, and even incontinence.

Breathing may be impaired briefly, and the individual might turn blue (cyanosis). After the episode, there's usually a post-ictal phase, where the person remains confused, drowsy, or unresponsive for several minutes. Tongue-biting—especially on the side of
 the tongue—is a strong clue to seizure activity. The individual often feels fatigued or disoriented for some time afterward.

Investigations typically include EEG, brain imaging (like MRI), and a referral to a neurologist. Treatment depends on the underlying cause and may involve anti-epileptic medications if the seizures are recurrent.

Fainting (Syncope):

Syncope, commonly known as fainting, is a temporary loss of consciousness due to a brief drop in blood flow to the brain. Unlike seizures, it is usually preceded by warning signs such as dizziness, nausea, lightheadedness, blurry vision, or a sense of warmth.
 These symptoms give a person a few seconds' notice before they lose consciousness.

During the episode, the person typically becomes pale and limp. There is usually no convulsive activity, though brief twitching may occur in prolonged fainting episodes (this is called convulsive syncope and can sometimes mimic a seizure). Importantly, recovery
 is rapid once the person lies flat, and they return to full awareness without confusion.

Fainting is often triggered by prolonged standing, emotional stress, pain, heat, or dehydration. Cardiac causes should also be considered, especially in older individuals or those with heart disease. The diagnostic approach includes ECG, blood pressure testing,
 and possibly a tilt-table test or Holter monitoring.

Clinical Distinction:

In summary, seizures and syncope can both result in a sudden loss of consciousness, but several key features help differentiate them. Seizures are more likely if there is post-event confusion, tongue-biting, or incontinence. Syncope is more likely if the event
 was preceded by warning signs and the recovery is quick and complete.

Both conditions can be serious, and anyone who experiences unexplained loss of consciousness should undergo thorough evaluation.

References:

Fisher RS, et al. (2005). Epileptic seizures and epilepsy: Definitions proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia, 46(4): 470–472.

Brignole M, et al. (2018). 2018 ESC Guidelines for the diagnosis and management of syncope. European Heart Journal, 39(21): 1883–1948.

Sheldon R, et al. (2002). Syncope and presyncope: Diagnostic approach. JAMA, 287(8): 1022–1029.

Kapoor WN. (1990). Syncope. N Engl J Med, 343(25): 1856–1862.

Lempert T, Bauer M, Schmidt D. (1994). Syncope: A videometric analysis of 56 episodes of transient cerebral hypoxia. Ann Neurol, 36(2): 233–237.

Hoefnagels WA, et al. (1991). Diagnostic accuracy of patient description, eyewitness report and characteristics of the ictal episode in differentiating seizures from syncope. J Neurol, 238(1): 15–20.

Shen WK, et al. (2017). 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients with Syncope. Circulation, 136(5): e60–e122.

Dr Geranmayeh