If they are doing it non stop, something is most likely stressing them. Whether it be another fish, water parameters, so on. What's tank size, stock, and parameters?
My fish tended to do it more often when young, I would say it is normal. I had one fish that liked to swim the horizontal length of the tank horizontally as fast as he could, man was that amusing.
haven't tested in a week or so but i do at least 2 30% water changes a week and don't overfeed. tank is cycled properly as it's been running for over a year. Temp reads 86.6* F and tank has much cover with many places for territory. The fish that seems to be doing is the biggest male. i'll go get a video of him in action