Stress was the biological, physiological, or psychological reaction of lifeforms to physical exhaustion, internal and external pressures or environmental changes. Methods for dealing with stress included plexing, (TNG: "Realm Of Fear", "Timescape") and making use of stress reduction programs. (TNG: "Realm Of Fear")
In 2151, Phlox speculated that Sluggo didn't eat due to the stress of no longer being in his native argon-rich environment. (ENT: "Fight or Flight")
According to T'Pol in 2153, Phlox was under extraordinary physical stress during his assimilation process by the Borg which could explain the voices he heard during this time. (ENT: "Regeneration")
In 2153, Trip Tucker told Captain Jonathan Archer that Chef was worried about the crew. They were skipping meals and he suggested it would be either too much work or the Xindi mission. (ENT: "Impulse")
According to Doctor Leonard McCoy's log, Captain Kirk showed signs of stress and fatigue just prior to his 2267 visit to the Shore Leave Planet. (TOS: "Shore Leave")
In 2268, Doctor McCoy noted in a medical log of Captain Kirk's indications of increasing tension and emotional stress, which were attributed to possibly being on patrol too long without relief and diversion. (TOS: "The Enterprise Incident")
While attempting to locate an older Arne Darvin on the USS Enterprise in 2268, Doctor Julian Bashir pretended to be doing a study on work-related stress, using "Ensign" Miles O'Brien as his test subject. (DS9: "Trials and Tribble-ations")
In 2366, Doctor Beverly Crusher noted that Tam Elbrun's blood pressure and glucose were indicative of general systemic stress. (TNG: "Tin Man")
By 2371, Starfleet Academy had a stress reaction test for its cadets. (DS9: "Facets")
A therapy for stress-related muscle tension was the osteopathic pressure therapy. (VOY: "Scientific Method")
By 2381, the Federation utilized ships such as the Dove as spas, which offered activities and treatments that were meant to reduce stress. (LD: "Room for Growth")