Is my fish just relaxing or what?

Puffy, my fish here at work, has spent the last 4 hours swimming about on his back at the surface. Before anyone says the obvious he's not dead, he's flapping his little fins about and appears to be having quite a chilled time, even doing cool spins every now and then. My worry is that I am busy being... show more Puffy, my fish here at work, has spent the last 4 hours swimming about on his back at the surface. Before anyone says the obvious he's not dead, he's flapping his little fins about and appears to be having quite a chilled time, even doing cool spins every now and then. My worry is that I am busy being impressed at his tricks whilst I should really be worrying he is trying to commit suicide or something..!

Is this normal behaviour?
Update: Thanks for all the answers, I got a bit worried with all the RIP Puffy comments, and started investigating online, and his symptoms are exactly like "Swimbladder" - not fatal but I have some ways to treat him. Puffy will live on! :-D
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