I moved this to the correct part of the forum for you.
There is only one thing that I can think of......is it hot inside of your house (or outside, wherever Onyx is kept)? This could be a reason for shaking and breathing heavy.
Also, was he running around a lot before he layed down?
Is it warm there, andhas he been running around and either it's humid, or/and a little warm?If after running around a bit, they are breathing rapidly it's normal.