Why do i start yawning and getting sleepy when i read my son his bedtime story?

(It doesn’t even matter if i’ve had lots of sleep, none at all or something inbetween…always do it…)

..Is it tribal thing… coz the yawning is supposed to be a tribal thing isn’t it?

Am I trying to tell him “it’s bedtime now hun” in a tacit way… me not even knowing I’m doing it either

Or is it that it just makes me tired?

Or something else?