The former glamour model, 35, revealed she's been feeling unwell for days with an unexplained illness that has left her feeling "so poorly".
The mum of four - whose youngest son Jett is only four months old - shared her misfortune with her two million followers on Twitter.
In the early hours of this morning (22 December), she tweeted: "Still soo poorly problem getting worse no meds are helping such s*** times :("
And then at around midday, she updated her fans with the message: "Great in hospital on a drip."
On the 19 December, she had first told the public about her illness, saying: "Feeling sooo poorly still ,im just not getting better doctors again this morning :("
Her many fans responded sending messages of support, with one writing "What's happened?!!! Xx" and another adding "Hope You Get Better Soon & Home For Christmas xXx."
Hours after being admitted to hospital for tests, Katie updated her Twitter account with the message: "Out of hos go back again in 48 hours mri scan had morning of needles my worst nightmare,time to concentrate on getting ready for christmas."
She has recently been in a war of words with ex-husband Peter Andre over who is supposed to be having their children at Christmas.
Katie again used Twitter to share her feelings. This time, in a fit of rage about Pete's festive plans with their kids, Junior and Princess.
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