I think you just rode beyond your limit.
Tunitas will do that to you. I have seen so many people suffer in that steep middle section, and I've experience it myself a few times. Welcome to the club.
I do a
53 mile, 5400' ride from Palo Alto up Kings Mountain, down Tunitas, right on Lobitos Creek, left on Highway 1, left on Tunitas.
Sometimes I feel great, sometimes I suffer in that steep section of Tunitas.