sudden siezers with with unconciousness foaming mouth and hardening of body.

[hilool]

One of my relatives aged 30yrs,suddenly from the age of 20yrs started experiencing sudden abrupt seizers starting with crying voice followed fy unconsciousness for few seconds.During this condition foaming occurs through mouth and body hardens and he falls down .this gets repeated sometimes 2 to 3 times a year or sometimes more frequently.Medical tests like EEG .MRI CS were carried out but showed no abnormality.Many neurologists were consulted ,  but till date nothing improved.Please help if any one can.