It was just switching itself off every 3 minutes or so and then rebooting itself with apple logo and switching itself back on.
It was pretty frustrating. It was doing this for around 4 days and now it's suddenly working again normally.
I took it to a shop and was told it had an error and needed to be sent off / replaced. I couldn't leave it there that day so I took it home and just continued using it the way it was and now suddenly it's fine again.
I'll still take it in to be fixed, but how random is this ? Has anyone experienced something similar ?