Found this while doing a search on it...

"You have been experiencing palpitations, which is the sensation of being aware of your own heart beat."

"Some measures you can take to help decrease these episodes in addition to medication includes, stopping your intake of caffeine and other stimulants"

Also read that it might occur more often if you dont sleep enough.

Came back to work this week after some time off and its been quite busy and I had too little sleep. Also been drinking quite a lot of tea and pepsi, someting I dont usually do. Will cut that out, have some proper sleep and see what happens.