Source: THE GLOBAL EDITION OF THE NEW YORK TIMES Oct 29, 2010
Article: Rangers' ace receives a rude dose of reality
A dictionary would tell you that a dose was a quantity of a medicine or drug taken or recommended to be taken at a particular time.
["Rude" here means abrupt.]
So the article implies that Rangers' ace hadn't realised what was happening until he was abruptly woken and made aware of his true plight. The headline might equally have said, "Rangers' ace receives a shot of reality".