Georgia Tennant has revealed her baby, who she welcomed in October, spent six days in hospital last week in an event which she has said will "haunt [her] forever".
The actress, who shares the tot and four other children with husband David Tennant, posted a black and white photograph of her baby attached to tubes in a hospital bed.
In the caption of the image, she thanked the NHS for all they had done for her and her family in the worrying situation.
She wrote: "Last Wednesday my NHS GP sent my baby to A&E after spiking a high temperature. Eyes rolling at this seemingly over the top reaction, reluctantly I trudged along, mildly coughing child in tow, to my nearest NHS hospital.
"We were seen within 10 minutes. After being checked over by 2 ‘over the top’ NHS nurses and another 2 ‘over the top’ NHS doctors, the now slightly lethargic baby was admitted. What ensued over the subsequent 6 days will haunt me forever but now back home, on the sofa, my baby tube free and pink again I take away one thing; our NHS is magic. An underfunded, understaffed and under threat sort of magic. Full of amazing people whose ‘over the topness’ puts people back on sofas together.
"I can’t thank you enough NHS and from now on my family will do all it can to help keep you together. Just as you did for us. #nhs @nhsmillion @cwpluscharity."
The Tennants share three other biological children, Wilfred, Olive and Doris, while Georgia has an older son Tyler from a previous relationship whom the Doctor Who actor has adopted.
Georgia is the daughter of actor Peter Davidson who played the fifth incarnation of Doctor Who.
She starred in an episode of the sci-fi series herself, playing opposite David in a 2008 instalment where she appeared as the Time Lord's artificially-created daughter.