Babies aren't able to verbalize how they feel and, early on, don't yet recognize that what they're experiencing has a particular cause. New parents also often have not yet learned the signals for "I am wet," "I need attention," "I need to eat" and "I am tired." Babies, even if they may not recognize cause and effect themselves, do signal what they need.
Babies who are growing tired tend to fuss. The more tired they get, the fussier they become. Overtired babies squirm, move their heads side to side and act agitated. You can bounce, hold and pat an overtired baby on the back, but those actions may increase the baby's agitation. Whenever the baby is fussy and refuses to be comforted, you need to go down the checklist from hunger, to needing a diaper change, to making sure nothing is poking or hurting the baby, to what just might be the problem -- the baby is tired but is fighting sleep.
Babies who are overtired may go from fussing to crying or skip the fussy stage completely and go right to screaming. New parents may not pick up on the "I am tired" cry at first, because all cries may sound the same. As you pay attention and listen, you'll start distinguishing the tired cry from other cries. This signal may be anything from a whimper cry to a full-out scream. The volume and strength of the cry depends upon how tired the baby is and his frustration regarding his inability to make you understand his need.
Refusal to Eat
Babies often signal they are overtired when, even if hungry, they refuse to eat. They may clamp down their lips and shake their heads to try to convey they aren't about to eat. Hunger isn't the most important need at that moment. Don't force a baby to eat. Instead, check to make sure the baby isn't teething or in pain. If you can't find anything else wrong, pick the baby up and rock, walk with or do those things for her that soothe and help the child fall sleep.
Older babies who can crawl have even less reason to sleep -- they are exploring a whole new world. As babies mature, they develop new ways to signal they are overtired. Babies who usually turn when you talk to them may ignore you. Babies may rub their eyes and tug on their ears. They may start bumping into things and fall over for no apparent reason. They may sit up or curl up with special blankets or toys and suck their thumbs.