The reality TV star, who is remembered for her barefoot performances on the show in 2010, told fans on Instagram that she was taken in by ambulance and that NHS staff had been wonderful.
Waissel shared a picture showing her in hospital, along with a newspaper headline saying “NHS ‘on its knees’.”
She told her followers: “Let me tell you, I was taken by ambulance yesterday for a suspected heart attack and @nhs @ldn_ambulance Watford general AND the ambulance services were / are amazing.
“I was initially told there was a wait by the ambulance call centre, but an ambulance was at my door within minutes.
"The entire team at Watford were/are beyond impeccable, and I am so grateful for your continued help!!”
The singer-songwriter, 35, went on: “So with this, if you’re experiencing a life threatening emergency, do not hesitate to call 999, they WILL come for you!!!”
Waissel’s fans inundated her with get well soon messages.
“Hope you have a speedy recovery,” one posted in the comments section, while another said: “Thinking of you and hope you get well soon.”
“Holy smokes. Hope you're okay!!” said another concerned fan.
Waissel found fame on the seventh series of Simon Cowell’s show and finished in seventh place.
The mum-of-one went on to make two albums and also competed in Celebrity Big Brother.
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