When my Wood frogs come up to terrarium glass and stare out, I like to sit at their level and observe their faces—especially when I have nothing else to do. However, I tend to notice that they will do as you described with your toad: they will breathe a few breaths and then pause for a few seconds, breathe again then pause, etc….They do this every time. It’s actually quite funny, as with each pause they could be thinking “What are looking at?”
I hope that nothing’s wrong with your toad and that abnormal breathing you observed was just something that happens normally—just like my Woodies— that you haven’t noticed before until now. Or maybe it could have just as LazyEyedFroggie said: he was frightened and needed some water to soothe him. As a dog is a man’s best friend, water is a frog’s best friend.
Take care,
-Autumn