Factual error: Nick tells fellow vampire Aristotle, "You still owe me for that time at the Battle of Hastings." Nick was brought across in 1228, or so the intro told us every week. The Battle of Hastings, as any British school kid knows, was fought in 1066, over 100 years before Nick's mortal birth. (00:29:30)
Crazy Love - S2-E26
Factual error: Dr. Shawna Welsh's medical degree, visible on the office wall behind her while she talks to Nick, misspells the name of Johns Hopkins Medical College as "John Hopkins." (00:08:35)
A More Permanent Hell - S2-E20
Factual error: In the first scene, Dr. Dana says the asteroid heading for Earth is 5 miles wide, "larger than the one that caused the dinosaur extinction." The asteroid that did in the dinos is estimated by most scientists to have been 6-8 miles wide. (00:03:00)
Factual error: Nat's god-daughter Cynthia Luce is buried within a few days of her murder with an elaborate headstone already in place. (In reality, headstones take months to produce.) But the wrong name is carved on the stone. It reads "In memory of Cynthia Lambert." (00:43:30)
Factual error: At the very end, Bridget Hellman is buried with a fully-engraved headstone in one just one day's time (which happens only in tv & movies: the process takes months in real life... er, death). She also spontaneously returns as a vampire without being "brought across," a violation of series canon, and she comes back mysteriously sporting 3 times more hair than she had as a mortal. (00:43:10)
Factual error: The cop who arrests Nick reads him his Miranda rights ("You have the right to remain silent," etc.) But "Forever Knight" is set in Toronto. At last report, Toronto rather resolutely insists upon remaining in the sovereign nation of Canada, where the Miranda Act, a U.S. Federal law, is not observed. (00:14:40)
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.