There's a kind of exhaustion, after your second and third winds have long passed, where you actually feel the neurons in your brain firing and missing one another. You wonder how much longer long you'll be able to form complete sentences before a force like a big hand descending from the sky crushes you flat and doesn't let you move, no matter how hard you try. As long as the cause of your exhaustion is enjoyable, and you're in the company of people who'll catch you if you fall, this can be a intriguing sort of altered state. You continue to function even as your thought processes are broken into little bits and snatched up by the big hand, and you're amazed at how strong you really are.
And I really was amazed. I've pulled my share of all-nighters, but none that involved hours of thinking about God and revelation. I hadn't planned to stay at my synagogue for the entire tikkun leil Shavuot, the traditional marathon of learning, but at about 2AM I understood that I couldn't leave, that it was necessary at this moment in my life to hear everything. In a candlelit room strewn with rose petals, we studied with eight different rabbis and teachers, and with each other in chevrutas, study partnerships, until we ran out of energy and could only listen.