If 2009 is any gauge it comes gently and then suddenly. Ripple effects of contracting credit take a long time to work through the economy, so it's important to heed observations of the bow shock. Fewer startups, lower credit card limits, no access to cheap corporate debt, cost cutting, more conservative consumer spending, all add up until one day you're chatting to a recruiter who is visibly sweating as he tells you he hasn't placed a candidate in months.

I was already senior back in 2009 too and it was ugly. If your bum is not already in a seat, right now it should be your top priority, and you should absolutely be vetting the kinds of companies making you offers.