I’d be pretty paranoid. My main concern would be to isolate myself from everyone as much as possible, which kind of sucks, since I’m already pretty introverted and not much for social activity. It’d also make dating afterward really awkward, as I’m not sure I could ever trust having anyone liking me again.
Safety deposit box for immediate storage of the ticket. Then, I’d contact financial advisors and lawyers recommended by my ex-fiancee’s family (a wealthy family, familiar with trust finds and such, and highly unlikely to try to scam any money from me), and resign my job. Weed out my Facebook friends and go private/unsearchable on it. Tell friends/family that are concerned by all of these actions that I had a windfall that was enabling all of this, and would discuss details with them when I felt comfortable doing so.
As of right now, I have a number of plausible reasons to do all of the above without raising much suspicion; my mom recently died, and it would be assumed that I received a decent insurance settlement. I did get one recent small settlement, and they know I’ve felt weird about receiving money for her death, so my reticence to discuss more money coming in would be expected. In addition, everyone knows that I’ve been wanting to quit work and go to grad school, so this would be the default assumption for everyone at work.
I’d be able to use my retirement funds and savings to move (and frankly wouldn’t need to keep many of my current things); pack up my collections and put them in storage, sell or give away my furniture, and then I’d go somewhere local but secure, a decent hotel or something. I currently live in a low-end apartment complex. I don’t have much family (and they’re all pretty trustworthy), and only a few friends whom I think are mostly trustworthy, but I wouldn’t be comfortable if neighbors found out I was going to have money, so it’d just be easiest to hit the reset button there. I’d also finally let my landline lapse (pretty inextricably linked to my real name by any sort of identity search at this point), and would probably change my cell phone number as a precaution.
At that point, I’d pull the trigger and claim the winnings. I’d be most suspicious of anyone from my past suddenly showing up (ex-wife, any of my ex-girlfriends, lapsed friends, distant family), and cat’s out of the bag everywhere else. Hopefully my isolation techniques above would keep things manageable. For very close friends, I’d probably see about setting up some sort of trust fund for them through my “handlers.” Then, I’d look at buying home(s) out of state/country – NYC, Toronto, etc. – where I’d feel comfortable having conspicuous wealth while remaining fairly anonymous, and then I’d move away from the current area permanently. There’s one old flame/current friend I’d love to sweep up with me, but would otherwise expect to go alone.