A 36-year-old man felt dizzy before bed. As he slept, his Apple Watch warned him of an unknown heart problem.

• A man was alerted by his Apple Watch that he had a heart condition: atrial fibrillation.
• The main symptom of atrial fibrillation is a quivering heartbeat.

A man went to bed after feeling dizzy and woke up the following day to alerts from his Apple Watch that he had a heart condition, BBC News reported.

Adam Croft, 36, from the UK, noticed last month his Apple Watch had been alerting him through the night that his heart was in atrial fibrillation — a type of arrhythmia that causes a quivering or irregular heartbeat.

Croft told BBC News that he called the UK non-life threatening emergency helpline, 111, for advice, who told him to get to the emergency room within the hour.

At the hospital he had two electrocardiograms, which measures the electrical activity of the heart, and doctors later confirmed he had AFib.

Croft told Insider he shared his story to raise awareness and make sure others take their symptoms seriously.

Atrial fibrillation can cause blot clots, stroke, and heart failure

AFib is a heart condition that affects at least 2.7 million Americans.

The main symptom of AFib is a quivering heartbeat, but can also include fatigue, dizziness, shortness of breath, anxiety, weakness, faintness, and sweating.

However, many people with AFib have no symptoms and their condition is only detected under physical examination, according to the American Heart Association.

Croft told BBC News that the night before his Apple Watch had alerted him, he had got up from the couch and felt dizzy. He went to get some water and "immediately felt the world closing in."

He ended up in a pool of cold sweat on the kitchen floor but went to bed.

Months prior to this, Croft said he'd felt "flutterings" of his heart but didn't think they were serious.

He said that he wouldn't have sought medical assistance if his Apple Watch hadn't alerted him, and assumed he was just getting sick.

AFib can be serious as it leads to blood clots, stroke, and heart failure in some cases, the AHA said.

According to the AHA, AFib mostly affects older people, those with high blood pressure or heart disease, people who drink heavily, athletes, and people with other chronic conditions.

They said that having a family member with AFib also increases a person's chances of being diagnosed.

Since being diagnosed, Croft has been offered cardioversion — a procedure that restores a regular rhythm — which he told Insider he hopes to have in the next few weeks.

In the meantime, Croft has been offered blood thinners because of the risk of blot clots, which can cause a stroke.

Croft told Insider that doctors have also said he should minimize stress in his life — as he'd had a stressful couple of years — and continue with a healthy diet and exercise.

He said: "It's made me far more likely to avoid stressful situations, and made me more aware of what's going on in my body. I'm much better at looking out for the signs now."