Jiraiya didn't know why he felt the urge to acknowledge Orochimaru's birthday. It still happened every year. He'd tense without knowing why, pause in whatever he was doing, be unable to write. He'd shift around, stretch his legs, try to get some blood pumping and clear his head with breathing exercises. The tension would come back, and then he'd finally realize it was Orochimaru's birthday in a day or so.
The day came around, and Jiraiya was inevitably sick to his stomach, lethargic, and unable to be roused to a state of enjoyment by just about anything short of really, really good food. For food, he'd get out of bed. But just barely.
Then the day would be over, and he'd shake it off with a shudder and go back to his everyday business.
Only to do it again next year.