Narcoleptic baby after 4 month shots

DS had his four month shots yesterday. He responded very well, and was his usual self all day, having had the shots at 10 in the morning. He also slept fantastic last night. Woke up at 2 a.m., which is two hours later than usual, and 5:30, which is usually when he would stay up, but he went back down until 7:15. Today he can't stay awake! He usually can last 1 hour 45 mins between naps. Today he is barely making it an hour! He's a little fussy, but I think because he's apparently so tired. Is it within typical parameters to have LO be so sleepy the day AFTER shots? I'm gearing up for a long night, if this is how we are spending the day...