Disorientation is a state of mental confusion as to time, place, or identity.
Amnesia is pathologic forgetfulness.
Example: As sometimes found in the infection-exhaustion psychoses, when the entire past of the patient may be wiped out for the time. Cases of permanent amnesia are known.
Aphasia is a defect in the interpretation or production of language.
There may be motor aphasia, auditory aphasia, vocal aphasia, sight aphasia; and with disability to produce words, they may yet be recognized when seen; or when they can be spoken they may not be recognized when heard; or with inability to speak them, they are accurately sensed by hearing; or though understood when heard, they are incomprehensible when read.
A delusion is a false belief which cannot be corrected by reason.
A somatic delusion is one centering upon alterations in the organs or their functions.
Example: Absence of a stomach, inability to swallow.
A nihilistic delusion is one which denies existence in whole or part.
Example: Mother denies the existence of her child.