Sudden may not be. Sudden at all if the episodes are ones that you "keep on having". It could be one of several kinds of seizures. Absence seizures act that way but are very brief and not noticed by the person affected. Dissociative episodes can last longer(large gaps of time not remembered) and are usually products of explosive anger or ptsd. In all cases medical evaluation is necessary. Don't put it off.
Get evaluated. May be you mean "forgetfullness" or "dificulty" to find words. The way our mind is evaluated is with an interview with a psychiatrist or mental health specialist. If you had an injury like head trauma amnesia is possible. Review all your medications. Alcohol and drugs may caused it. Stroke and dementia could be in the differential as brain tumors.
Memory loss. See your family doctor for an examination. If you have a problem you can be referred for proper treatment.