Keep an eye on margin debt (i.e., borrowing against one's stock holdings and owed to a brokerage house). In nominal terms it is indicating trouble, while in real terms, less so. In 2006-2008 many got caught short when the US equities market turned around, and the selling fed upon itself, as can happen when investors are forced to unwind their positions quickly. It was a sickening ride for those who watched, and even worse for those who were on the ride at the time.
Pro tip: back down your levered equity positions NOW. Your broker will thank you. And if you have Robinhood on your phone, close your account, get out and delete the app. The investment world is no place for folks who no not what they are doing...
Just keep it off the 59. Like Jan and Dean sang, the 59 in Houston is no place to play...