Suddenly can't ride with no hands on my bike , what's wrong?
 

I use to be able to bike for like 10 minutes straight with no hands at all, up hills, turning, everything perfectly straight at any normal speed.
Starting Around last week, when I let go of the handle bars, I can't seem to ride with no hands at all unless I'm going SUPER SUPER fast. It just suddenly sways to the left.
What is wrong?

Bent frame, misaligned forks, inner ear infection, new medication, stroke, etc.

Does this happen on all bikes or just one?

Fear.

Just this one. It's not me. It's something with the bike but I don't quite know what.

If it's mechanical, it's not safe and you shouldn't ride it til you figure it out and get it fixed. People get killed by screwed up forks.

Check your headset adjustment. I've had that happen if the headset is binding.

If it's worked it's way to being too tight, or possible dry bearings, it tends to "hold" the steerer into position. The natural tendency of the rake in the fork to straighten out the wheel will no longer work.

Since you have stated that you haven't had this issue before with other bikes and that this just started about a week ago... I gotta ask- how long have you had this bike?

Loose or tight headset. Loose front skewer. Loose wheel bearings. Cracked axle, fork, or frame. Very loose spokes. Flat tire.

Hold on to the handlebars , with at least one hand... problem solved.

Have you removed either of the wheels recently?

i was thinking wheel not in straight
as j c koto is implying

otherwise
all the other mechanical problems mentioned above are possible
as is bent frame or fork from a recent crash
or other abuse

Here you go.

Rear wheel slightly out of alignment was my first thought.