Euphoria was a condition in which a person experienced intense feelings of happiness, ecstasy, and joy.
In 2266, while performing a mind meld on Simon Van Gelder, Spock told him that he would "begin to feel a strange euphoria". (TOS: "Dagger of the Mind")
In 2268, Doctor Ann Mulhall believed James T. Kirk was suffering from a form of false euphoria after his mind had returned to his body, having briefly exchanged places with Sargon's mind. (TOS: "Return to Tomorrow")
In 2269, Lieutenant Uhura relieved Montgomery Scott of temporary bridge command. This was due to his "euphoric state of mind" while in orbit around the second planet of the Taurean system during the absence of Captain Kirk and landing party below. (TAS: "The Lorelei Signal")
In 2368, Riley Frazier, Orum, and other Borg drones initially experienced euphoria after being released from the Collective. However, this wore off once they realized how different they were to one another. (VOY: "Unity")
In 2370, a replicant of Miles O'Brien sarcastically claimed that he was experiencing "lots of euphoria" while being examined by Julian Bashir. (DS9: "Whispers")
The Erosene winds of the planet Alastria were said to evoke euphoria in those who encountered them. (VOY: "Prime Factors")
In 2372, after Tuvok's abilities to suppress his emotions had been temporarily removed by The Doctor, the Vulcan said he felt "quite euphoric". (VOY: "Meld")
In 2374, Weyoun 5 said he didn't share Dukat's euphoria, when Dukat believed victory had been achieved despite the Dominion's loss of the Bajoran wormhole and Chin'toka. (DS9: "Tears of the Prophets")