too much pressure

yesterday morning as i was crossing the yard at work i made the customary greeting to a co-worker, "good morning".
he responded by saying, "how are ya?"
now i'm under pressure.
does he really want to know or is he just greeting me?
do i need to tell him how i am doing? after all we are just two guys passing in the rain.
do i need to ask him how he is doing? i once read an article about people who don't enquire as to the welfare of others. they were selfish and self-centered. i certainly don't want to be perceived as selfish so i guess i should ask him back. but now it's a second greeting. now we have to stop.
and does he really care anyway?
am i going to be a slave to the socially proscribed roles?
what if he really is having a bad day and i don't ask?
do i really want to hear about his bad day?

maybe next time i'll just pretend to be looking at my paper. too much pressure.