Concerning behavior.

Hello everyone. It's nearly lights out time for my tank but walking by I found one of my guppies laying on the substrate. Watching it he seemed to be alive but I didn't want to risk leaving a dead guppy in overnight and the ammonia that would cause. So I reach in with some aquascaping tongs and gently touch his dorsal fin... he takes off to the the back of the tank.
He's alive, good. But it's still concerning to be he was laying on the substrate. So I check the perimeters of the tank:
pH: 7.8, Ammonia: 0.0, Nitrite: 0.0, Nitrate: 10-20
This is actually better than I expected as it's been over a week since my last water change... the plants must be doing quite a lot of work.
No pics because the fish love darting right when I take the pic to make it blurry. He's a mostly orange fancy guppy with a white belly... his belly became white after I got him but it's just been consistently his belly not spreading anywhere. He has fin-nipping damage but not white fringes on the fins suggesting finrot.
As I was testing he resumes usual behavior, schooling, playing ect with the other guppies but I noticed that when he wasn't actively swimming he'd tilt backward as if the back-half of his body was heavier than the front.

 

He might have just been sleeping. They do that sometimes. My endlers are always sleeping on the substrate, giving me a scare until they wake up.

But if he consistently shows buoyancy issues while awake then yes, something might be amiss.

 

My guppies with larger tails sometimes tend to tilt backwards, so I try to give them places with less water flow to make it easier for them.

As for the staying still than darting thing I agree he might have been asleep, from the way you describe it it sounds like that’s what it is, I’m not 100% sure though, so keep a close eye on him for sure.

 

I have guppies and have seen them sleeping on or just above the substrate so i think your okay especially since it was alert when you touched it.

 

Thanks for the responses everyone. I'll keep an eye on him. Hopefully he was just sleeping.