That is completely fine and is often expected especially during the first couple sessions. Some pets completely relax and sleep throughout, and sometimes carry on sleeping deeply after. For others the sensations they may feel, and the unusual way an unfamiliar human is touching them, could feel intense at times and so they may need to break away and move around for a bit. That is absolutely fine. Remember how dogs have been training us over the years how and where to stroke them? They may keep trying to get me to stroke them the way they want me to, but I would have to gently decline and work on those sensitive areas in order to help them.