Katie Price was torn from Harvey's side in intensive care and the next 48 hours are "critical".
The former glamour model, 42, was left with no choice but to head home while her son, 18, remains in intensive care in a stable condition.
Doctors are watching Harvey round-the-clock and he will undergo a series of tests.
Harvey's temperature spiked and he had major problems breathing.
A representative for Katie Price told MailOnline : "He has had chest pains and a temperature. An extremely high temp. It was 42. You could cook an egg on him. It spiked quickly and he's had major problems breathing.
"The next 48 hours are critical. Harvey just really needs to do well over the next couple of days. He is having loads of tests today and being watched around-the-clock."
It has been devastating for the mother-of-five as she cannot stay at her son's hospital bedside because of the strict rules surrounding coronavirus in place.
Katie headed home to get a shower and change while she waits patiently for news on her son.
Sadly having had the experience of situations like this before, the reality TV star has gone into autopilot "robot mode".
A representative for Katie told OK! magazine : “Katie's gone into robot mode – unfortunately she has been in these situations a few times before.
“She can't stay with him in intensive care in hospital so she's come home to have a shower and a change.”
But Katie has been seeking comfort from close friends and fans alike.
On her arrival home, the reality queen kept her admirers in the loop about her son's condition.
Katie thanked her legion of loyal followers for their kindness and love for her son at this difficult time.
She tweeted: "Thanks so much for all your messages of love and support for Harvey. It’s really keeping me going."
Harvey was rushed to hospital over the weekend after struggling to breathe and was said to be at risk of organ failure.
Katie kept her fans in the loop as she confirmed her son was stable and in the care of hospital staff at an intensive care unit.
She wrote: "I can confirm Harvey is in intensive care and in the best hands and would like to thank the ambulance services and the hospital staff for the quick response and making him stable."
Harvey was struggling to breathe and had a high temperature when Katie alerted 999.
A representative for Katie told The Sun : "His condition is very dangerous and Katie is terrified.
"He has a temperature of 42 degrees and is struggling to breathe.
"One of his conditions is adrenal failure that could cause his organs to fail and is very dangerous."
Just weeks ago Harvey - who has Prader-Willi Syndrome and partial blindness - was dashed to hospital mid-way through his sister Princess' 13th birthday bash.
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