My best guess, a combination of things piling up:

• For some time, I've been reading through an EPUB of the Sequences (and am currently 47% of the way through), which has generally kept LW-style thoughts high in my mental queue.
• For about three and a half months, I've been aiming for writing near-daily chapters of a rationalist fan-fiction, which has pushed me to thinking even deeper about such matters.
• Last month, my uncle had a heart attack, which required him to be revived five times before we even found out about it; since he got out of the hospital, we've been trying to help him adjust his lifestyle.
• A few days ago, an article appeared in my newsfeeds about a woman with cancer receiving donations to fund her cryo-preservation. This prompted me to do some browsing on cryonics, which I've done before; this time, though, I actually comparison-shopped between the providers, looking at what it would take to make the arrangements, and how much it would cost.
• I found out that arrangements could be made for under $30 per month. I'm on a fixed income, but there's enough slack in my budget that even I can afford that if I wanted to make it a higher priority than, say, a monthly movie-and-a-restaurant indulgence.
• I subscribed to a few cryo mailing lists, mentioning in one subscription request that I was looking into this and leaning more towards CI than Alcor.
• I finally decided that, if I was going to go for cryo, I'd go for CI over Alcor.
• I sent an email to CI, asking for further info on some details.
• I still hadn't fully committed, so I recalled a suggestion or two I'd heard on making decisions you've been pushing off making - and posted here, making a public commitment to arranging cryo. No forms have been signed, no money has been sent to CI or the insurance company - but I now consider it only a matter of time until all that is done. Before I made the post, I was still hedging my bets and getting ready to back out if I changed my mind; but now I'm weighing all my decisions with the assumption that it's only a matter of time before it's all official.