Final answer:
Robert experienced a night terror, involving panic without memory of the event, while Fred had a nightmare, with a vivid recollection of the dream.
Step-by-step explanation:
Robert likely experienced a night terror, whereas Fred experienced a nightmare. Night terrors are a sleep disorder in which the sleeper experiences a sense of panic and may scream or attempt to escape from the immediate environment, typically occurring during NREM sleep.
These events are characterized by a rapid heart rate, seeming awakeness but with no subsequent memory of the episode. In contrast, nightmares are vivid, distressing dreams that typically occur during REM sleep and can often be recalled in detail upon awakening. The correct answer to the fill-in-the-blank question is: a) Night terror; nightmare.