Seizures are of many types:
- tonic (stiffening)
- clonic (jerking)
- combinations of both tonic and clonic
- loss of awareness
- myoclonus (sudden jerks of the whole body or limb)
- abnormal feelings of fear, smell, taste, vision and/or feeling in a part of the body with or without impairment of consciousness, all pointing to a focal onset (specific part of the brain from which the seizure originates)
- automatic movements (such as fiddling with clothes or objects, mumbling or making chewing movements).
All types of epilepsy have a small risk of sudden unexplained death (known as sudden unexpected death in epilepsy (SUDEP)), which is difficult to anticipate but has brought about the development of epilepsy networks and guidelines for effective diagnosis, investigation and treatment.
The more severe syndromes include a number of conditions that may be difficult to treat and which cause severe regression (loss of acquired skills) relating to learning, social functioning and behaviour.
Thus, learning impairments (see entry Learning Disability), autism spectrum disorder (see entry Autism Spectrum disorders, including Asperger syndrome), attention deficit hyperactivity disorder and other behavioural disorders are very common in children with intractable seizures (seizures that are difficult to control).
The regression in development, which is particularly caused by early-onset epilepsy is known as an epileptic encephalopathy. This is particularly related to sub-clinical epileptic activity (activity that is not obvious) rather than the rate of obvious seizures.