Generalised onset seizures

Generalised seizures 

A generalised seizure (or generalised onset seizure) affects both sides of the brain from the start. It causes you to black out (lose consciousness). Sometimes, the period of unconsciousness is so short it may not even be noticed. 

Before a generalised seizure, you may have unusual symptoms that could be a sign your seizure is starting. This warning is also known as an ‘aura’. It’s likely that this warning will happen at the beginning of the seizure in just one part of the brain, before it spreads to the whole brain. If you do get this warning, try to get into a safe place, even if that’s just sitting on the floor.  

Seeing anyone have a seizure can be quite frightening. It can be especially worrying when the person having a seizure is a baby or child. But it’s important to remember that if they’re unconscious during generalised onset seizures, they will not be aware of what’s happening, and they usually recover quickly. 

Tonic-clonic seizures 

Tonic-clonic seizures used to be called grand mal seizures. They are the type most people recognise. 

Tonic-clonic seizures are caused by abnormal electrical activity which affects the whole brain. This type of seizure usually comes with reduced awareness or a complete loss of consciousness.  

The name ‘tonic-clonic’ describes the physical symptoms that occur during the two phases of the seizure – the tonic phase followed by the clonic phase. We describe each of these phases in the sections below. 

The tonic phase 

A tonic-clonic seizure starts with the tonic phase. During this phase you may become stiff and fall to the ground. Sometimes you may bite your tongue, make a brief crying sound, and may become unconscious.  

The tonic phase may last about ten to 20 seconds.  

The clonic phase 

The clonic phase usually comes next after the tonic phase. During this phase, your arms or legs may begin to jerk. After a few minutes, the jerking slows and stops, and the muscles relax.

After the seizure, which usually lasts around one to three minutes, you might be drowsy, confused and agitated and take some time to return to normal. You may also have wet or pooed yourself or have bitten your tongue. Often, you will feel exhausted and need to sleep.  

If a tonic-clonic seizure lasts for five minutes or more, this is called status epilepticus and needs emergency treatment. If you have repeated seizures (e.g. three or more in 24 hours), this also needs emergency treatment. Talk to your doctor about what exactly this means for you.  

Find out more about emergency medication for seizures.

Absence seizures 

Absence seizures often begin in childhood and do not usually continue into adulthood, although they do continue in some types of epilepsy.

There are two types of absence seizures – typical and atypical. We describe each of them in the sections below. 

Typical absence seizures 

In typical absence seizures, you may do the following things:  

• shut off and stare blankly into space for about 5 to 10 seconds 
• breathe quickly (hyperventilation) 
• not respond to anything 
• stop talking in the middle of a sentence 
• be unaware of what's happening around you 
• flutter your eyelids, fidget with your hands or walk around aimlessly

These things can happen many times a day. Then, you will snap back, continue what you were doing before and be unaware of the seizure. 

Often, other people might not even notice these episodes. If you’re at school, it's possible that staff may mistake absence seizures for not paying attention or daydreaming. This may happen if they do not know how seizures can affect children. Because of this, children with absence seizures may find it hard to learn and keep up at school because they miss information. 

If you don’t believe your absence seizures are being taking seriously in class or they are impacting your learning, read up on the support you are entitled to. If you’re a parent or carer, you can also talk to the school if you’re worried about this.

Typical absence seizures are linked with clear changes in electroencephalogram (EEG) test results. Doctors will use EEG tests to help work out if you are having typical absence seizures. 

Atypical absence seizures 

Atypical absence seizures do not usually start or finish as quickly as typical absence seizures. They usually last longer, and you might have changes in your muscle tone that cause small movements, such as nodding your head slightly or chewing.

Sometimes, you may continue to respond to your surroundings during an atypical seizure. Atypical absence seizures are also often linked with other seizure types and learning disability.  

Myoclonic seizures 

Myoclonic seizures can be both generalised (affecting both sides of the brain) and focal seizure types (affecting one side).  

You are usually awake during a myoclonic seizure – this can often happen just after waking or when you are tired before going to bed.  

The name of this seizure describes what happens during this type of seizure: 

• ‘Myo’ means ‘muscle’ – the muscles tighten rapidly.  
• ‘Clonic’ means ‘jerk’ – a burst of abnormal electrical activity in the part of the brain that controls the muscles causes sudden jerking in the head, arms, legs, neck or body.  

During this type of seizure, you might also roll your eyes, blink, nod, make coughing sounds, or fall to the ground (if you’re standing).  

Myoclonic seizures happen in a variety of epilepsy syndromes, such as juvenile myoclonic epilepsy syndrome.

Tonic seizures 

Tonic seizures can be generalised (affecting both sides of the brain from the start) or focal (they start in one side of the brain).  

The name ‘tonic’ means an ‘increase in tone or tightness’ of the muscles.  

During a tonic seizure, the muscles in your chest, arms and legs may contract rapidly, causing your arms, legs and body to become stiff (rigid). Your back may also arch and your breathing may change. Changes to your breathing, may mean that your skin colour changes slightly, for example the skin around the mouth may look blue. This is because your lungs are getting less oxygen. 

You might also lose consciousness and fall to the ground. Once the seizure has stopped, you regain consciousness and your muscle tone goes back to normal. 

Seeing someone have a seizure can be very distressing but remember that they often do not last for very long. Tonic seizures are generally short (less than a minute) and the person will recover from them quickly.  

People with Lennox-Gastaut syndrome are more likely to have this type of seizure. 

Atonic seizures 

Atonic seizures can be generalised (affecting both sides of the brain from the start) or focal (they start in one side of the brain).  

Atonic is the opposite of tonic, so during an atonic seizure muscle tone is reduced, which causes you to suddenly flop forward and fall to the ground. This is sometimes called a ‘drop attack’. In babies, atonic seizures most often appear as a ‘head drop’.  

During an atonic seizure, you may lose consciousness for a short time. But you usually recover quickly.  

If you are at risk of atonic seizures, or they happen often, you may need to wear protective headgear, such as a helmet. This is because of your risk of injury from falling or losing consciousness. 

People who have other seizure types, such as tonic or myoclonic seizures, may also have atonic seizures.