How to float in water for 5 minutes?

Like any kind of floating? If you can do a nice backstroke, you will be able to float fine. I am a backstroker and to float, i just lay back, stay calm, and just watch the clouds. I guess something that will help is to keep a lot of oxygen in your body. But anyways, the main thing is to just stay calm and relax to float. You don't wanna go crazy and start sinking.