I've been having the exact same feeling lately...it's really
weird. Wide, sweeping turns (at any speed in either direction) that only a few months ago I wouldn't even have noticed making, now give me pause and I throttle back and sometimes just get convinced the bike is going over, when I KNOW damn well it isn't. My bike is perfectly sound mechanically, but the ONE thing that has changed in my life is my stress level.
Under A LOT of pressure at work as we're opening a brand new facility in less than two weeks, and a lot of the responsibility for making sure it goes right is on me. My stress level is 10 times what it was 6 months ago, and in that time I've noticed exactly the feeling you're talking about--almost to the point of micro panic attacks that last one or two seconds. More than anything, they really piss me off, because I KNOW how to ride and I KNOW my bike is fine.
It's probably a good thing I have a full face shield on my helmet, otherwise the cagers would think I'm nuts as I actually yell at myself like "What the Hell's wrong with you? That's nothing! Stop it!"
Stress does really weird things to the mind AND the body. In my case, I can see NO reason for the doubt other than the stress increase in life is manifesting itself as a sense of being unsure. I still ride every day I can and I refuse to let it beat me... and I'm betting mine goes away after May 31st (opening day)...
But stress is an evil bitch...and I can't wait to dump her.
Relax & enjoy the ride,