When I started refereeing a very wise and experienced colleague gave me this piece of advice " if a player goes down and is quite still then be very concerned and go to him immediately; if he is rolling about and making a lot of noise there is probably very little wrong with him. " Not infallible but I found it to be a pretty accurate rule of thumb during my officiating career. Another refereeing friend, who was on the FL for many years once said " remember most, not all but most, players will try and con an advantage out of you . They are not on your side " Very prescient words.
Of course, not being there I cannot comment accurately about this specific case at Northampton.