Delayed onset of concussion symptoms is very common.  The only symptom that is common in the immediate post-injury time frame is that of “alteration of mental function”, i.e. “brain fog” or worse.

Mayo Clinic recognizes, in its patient informational bulletin regarding concussions, that the symptoms can develop over the course of days, weeks, months, and even years.

Some symptoms commonly develop earlier than others.  The concussion symptoms of US soldier in Iraq recently developed over a 30 day period.Balance/dizziness, nausea, headaches and memory problems tend to be early-onset symptoms.  Conversely, irritability, sleep dysfunction, and fatigue tend to have a delayed onset, in some cases due simply to the chronicity that “wears down” the victim.