Anxiety, also known as worry, apprehension, concern, being on edge, or nervousness, was an emotion characterized by having a sense of fear despite no immediate threats being present. Those with a phobia experienced anxiety towards a particular thing or concept.
Naomi Wildman was minorly anxious while her mother Samantha Wildman was on an away mission for a few days, due to the fact that the mission was dangerous. Neelix rated her anxiety on a scale of one to ten, with ten being the most extreme, and said that Naomi's anxiety was at about a level five. (VOY: "Once Upon a Time")
Those with post-traumatic stress disorder experienced anxiety associated with memories of a traumatic event.
Both Hoshi Sato and Reginald Barclay expressed anxiety before using the transporter for the first time because they were afraid of being deconstructed on a molecular level. (ENT: "Vanishing Point"; TNG: "Realm of Fear")
When The Doctor went on his first away mission, Kes wondered if he was nervous. The Doctor replied that he could perform emergency surgery and make life-or-death decisions without getting nervous and asked Kes why she thought he might be nervous. She replied that those things were familiar to him so he might be nervous of the unfamiliarity. (VOY: "Heroes and Demons")
When Elim Garak had to do repair work in a crawlspace, he felt extremely anxious due to the fact that he was claustrophobic and it was a confined space. He tried to reassure himself, but when his lamp went out, he lost control and ended up fainting. However, when he regained consciousness, he was able to do it successfully despite his anxiety. (DS9: "By Inferno's Light")
When Timothy was experiencing a short temper after being taken on board the USS Enterprise-D after the starship he grew up on exploded, Deanna Troi noted that she was very worried about his behavior. (TNG: "Hero Worship")
When Tressa, Corin, and Elani were on the surface of a moon for the final stage of their lives, they became anxious that the Morrok would take them and kill them. Tuvok speculated that this anxiety was making them imagine that this possibility was more likely than it actually was. (VOY: "Innocence").
When Tuvok, Neelix, Sklar, and others were trapped in a space carriage and running out of oxygen, Tuvok told Sklar not to focus on situations beyond his control as that would make him more anxious than he already was. (VOY: "Rise")
While on an away mission in a deserted Borg ship, B'Elanna Torres felt nervous. When Tuvok told her that becoming apprehensive might negatively impact her, she replied that she was not apprehensive, just "nervous as hell", despite nervousness and apprehension essentially being the same thing. (VOY: "Unity")
When the Voyager crew had to be put in stasis for a month to protect themselves from the effects of a radioactive nebula, sans the doctor and Seven of Nine, both Tom Paris and Chakotay were apprehensive. Paris was nervous because he was claustrophobic and the stasis chambers reminded him of coffins, and Chakotay was because he did not trust Seven of Nine to be in charge. Later, Seven of Nine became extremely anxious due to her fear of being alone, something she had experienced once as a Borg drone previously. When he was released, Paris was slightly apprehensive about his soup due to not knowing what was in it. (VOY: "One")
When B'Elanna Torres was running dangerous holodeck programs with the safety turned off, Janeway became concerned for her well-being because she believed Torres was deliberately trying to injure herself and therefore had psychological problems. (VOY: "Extreme Risk")
When Janeway was planning to steal transwarp coils from a Borg sphere, she suspected Seven of Nine to be anxious because Seven was distracted and making mistakes. Seven replied that she was unsettled due to her memories of being a drone. (VOY: "Dark Frontier")
Before performing for the Qomar, The Doctor felt apprehensive. The apprehension he felt was not typical "stage fright", but rather anxiety at the prospect of exposing a culture to a new concept (namely music) for the first time. (VOY: "Virtuoso")
Following contact with a memorial to the Nakan massacre, Harry Kim experienced what The Doctor described as an anxiety attack. Many of the Voyager crewmembers began experiencing similar symptoms as the vessel moved within range of this Nakan memorial on the planet Tarakis. (VOY: "Memorial")
Occasionally, anxiety produced a tingling sensation in the abdomen, known as "having butterflies in one's stomach". When Icheb was meeting his parents for the first time since being rescued from the Borg, he felt anxious, which was accompanied by a sense of "butterflies in the stomach" that he mistook for a medical condition; however, The Doctor told him that he was in perfect health. (VOY: "Child's Play")
In the story Neelix made up to entertain Icheb, Mezoti, Azan, and Rebi while Voyager's main power was turned off, Neelix felt anxious due to being afraid of being inside nebulae and they were passing through one. He wondered if the rest of the crew were anxious too, but Tuvok said that they were not, reassured him that the nebula was safe, and suggested he install curtains. (VOY: "The Haunting of Deck Twelve")
When Seven of Nine was somewhat unsuccessfully attempting to play a holographic piano in an emotional way, a holographic Chakotay asked her for her emotions. She replied that she was anxious and also frustrated. (VOY: "Human Error")
When the Borg queen appeared to be attempting diplomacy with the Voyager crew, Harry Kim and Chakotay asked why she did so, as Borg generally were not diplomatic. Janeway suggested that the Borg queen was worried and was attempting to find out what the Voyager crew was planning on doing. (VOY: "Unimatrix Zero")
When Picard ordered a sudden course for the neutral zone, Data remarked how he was glad to be unable to feel emotions, since otherwise, the order would have made him feel very nervous. (TNG: "Data's Day")