as far as water parameters go, i can only give you the ph..7.0.., i have yet to get a test kit. stressed? well, i'm not to sure. it gets into fights with my scissortail rasbora on occation.
My Serpai tetras do this from time to time especially when there is a light source coming from outside. For example if the lights are off in the aquarium and i got lights on in the room they will swim on a slant so the top of thie body is towards the light. These types of tetras do this more than anybody....I dont think it is anything to be concerned about if no other symtopms are being displayed.
My tetras and my tiger barbs do this - usually at night and usually behind a plant or the heater tubes. I think they are just "resting" when they are in this position.
Notice I did not say "sleeping"! Didn't want to spark any debate on THAT topic!