Rainbow boa, behaviour change

Hi just after some help and advice please, I own a male rainbow boa and he is about 22years old and normally very active and easy to handle. I have had him since baby and never had any problems before.
But in last week he has gone under shelf in cooler end and hasn't moved very much and he is very defensive when tryed to get him out, his temperature and humidity hasn't changed and he looks healthy in himself, so just wondering if anyone had similar problem or any reason to why he behaving odd