Lucy Letby went salsa dancing the night after she allegedly tried to murder a baby boy, a court has heard.
The 32-year-old is accused of the murder of seven babies and the attempted murder of 10 others when she worked as a nurse at the Countess of Chester Hospital between June 2015 and June 2016. She denies the charges.
On Tuesday, the jury at Manchester Crown Court heard she added insulin to Child F's intravenous feed bag less than 24 hours after she allegedly murdered his twin brother in the hospital's neo-natal unit.
The baby boy's heart rate surged and his blood sugars dropped dangerously low after the feed on 4 August 2015, the court was told.
His parents were "keen" to move him out of the hospital earlier in the day after the death of their son, Child E, on the previous night shift but were told no transport was available.
Following the end of the night shift, in which Letby is accused of poisoning Child F, the defendant messaged a colleague - who cannot be named for legal reasons - showing concern for the child's low blood sugar.
She wrote: "Something is not right... he's a worry."
Letby, 32, then sent a message to another colleague, Minna Lappalainen, on the evening of 5 August.
She asked: "Are you going to salsa tonite?"
Her colleague replied: "Should do really as I have not been for ages. Meet at TF 2020?"
Letby replied with an OK emoji, before adding: "Need to try and find some post nites energy."
Ms Lappalainen responded: "Don't have to stay late."
To which Letby answered: "Hasta luego."
The unidentified nursing colleague later messaged Letby from the hospital to say Child F was "a bit more stable", adding that medics were "trying various tests to try to find answers".
Letby replied: "Oh dear. Thanks for letting me know."
Her colleague said: "He's defo better tho. Looks well, handling fine."
Letby later asked: "Wonder if he has an endocrine problem then. Hope they can get to bottom of it.
"On way home from salsa with Minna. Feel better now I've been out."
Letby had a house-viewing appointment the following day, the court was told, and Child F went on to recover several days after the night shift incident.
His elder brother, Child E, born a minute earlier, was allegedly killed with a fatal injection of air into his bloodstream.
Letby is also accused of murdering another set of twins, her first two alleged victims, in June 2015, jurors have heard.
She allegedly killed Child A by administering air into his bloodstream and then attempted to murder his sister, Child B, using the same method on the following night shift.
The trial continues on Wednesday.