open ur snakes mouth and if u see excess saliva then he is sick. if it is pretty bad u can use a q-tip and wipe it out of his mouth to help him breath. when ur holding him do u feel anything coming from his lungs? most times u can feel something when they "pop" while breathing. let him rub his face on ur hand or something and if he leaves a streak of thick/slippery mucus that is a sign. also check for retained shed or snot in his nostrils cuz that can cause noises.raise ur temps and humidity a bit n try soaking him for about 30 min a day. it can help them breath and sometimes they can cure themselves but a vet appt is needed. when u go to the vet tell them u want a culture done first to test what is making him sick. they will prolly give u some antibiotics until the test results get back