Mysticism isn't a topic that LW has paid any attention to.
Meditation has received some attention here, though I can't think of other sorts of mysticism. Perhaps Crowley's writings.
Would you please refer me to the discussions on meditation you're thinking of?
This is a sticky subject. "Meditation" and "mysticism" differ from context to context. E.g., Christian mysticism (the telos of which is union with God) and what Crowley meant by mysticism are fundamentally different (the latter sharing more in common with Hindu yogi praxis where union or samādhi is not necessarily restricted to a Diety; and in Buddhist mediation the purpose of samādhi is subsumed under a different goal altogether.). Meditation can refer to ...
To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).