Prime Minister Tony Blair has suffered a reoccurrence of supraventricular tachycardia - a heart "flutter" - which can leave the patient with palpitations, shortness of breath and dizziness.
He will return to hospital on Friday for further treatment, having originally been admitted in October last year.
BBC News Online's Tristram Biggs, 32, describes his treatment for the same condition.
I was woken up in the middle of the night by a racing heartbeat, sweating heavily and feeling slightly faint.
Bemused and slightly shaken, I went to my computer and immediately asked Google what were the symptoms of a heart attack.
My symptoms had stabilised, but as I read about shooting pains in the arm and shortness of breath I started feeling worse again.
My heart was racing at about 200 beats per minute, and I was definitely feeling faint.
I felt like sitting down, but had to walk around because of the adrenalin.
"An SVT is basically an interruption in the regular electrical signals from the brain to the heart"
So my wife suggested we call her sister, who luckily for me is a doctor.
Despite being woken at 0230 she listened patiently to my symptoms and told me not to worry.
A supraventricular tachycardia, or SVT, is basically an interruption in the regular electrical signals from the brain to the heart.
It is reasonably common and generally harmless.
The symptoms can be cured by an injection at any hospital, but my sister-in-law suggested I dunk my head in a sink of cold water.
Apparently the shock would probably "reset" the signals and bring the heartbeat back to normal.
In fact, listening to the description of the mundanity of the condition calmed my heartbeat for me - after 15 minutes I felt perfectly normal and went back to bed, head still dry.
However it was definitely a nasty shock.
I did subsequently visit my GP to have my heartbeat tested and nothing irregular was found - hopefully that will be the last time I get woken up in that way.