Did anybody else's kids start waking up crying at 9 months old for no reason that we know of? Just…

Did anybody else's kids start waking up crying at 9 months old for no reason that we know of? Just over the past week, my son has started waking up 2 times every night crying and going back to sleep only when Daddy put him back to sleep. Could it be a nightmare, growth spurt, or teething? Please help.