You should watch:

Realm of Fear

This was episode number 2 of season 6.

The following characters appeared in this episode:

(as Thomas Belgrey)Crewmember
(uncredited) Ensign Jae
(uncredited) Ensign Kellogg
(voice) Enterprise Computer
Admiral
Barclay
Captain Jean-Luc Picard
Chief Miles O'Brien
Counselor Deanna Troi
Commander Wiliam T Riker
Doctor Beverly Crusher
Lieutenant Worf
Lt Commander Data
Lt Commander Geordi La Forge
Nurse Alyssa Ogawa