Keep walking after releasing W key in WoW

I started playing World of Warcraft and I don't know what I did that I kept walking in one direction after releasing the W key. I've tried to repeat this behavior, like clicking in the horizon, but I was unsuccessful.

What is the shortcut or way to keep walking in one direction without keeping pressed the keyboard constantly?

Num Lock should toggle continuous walking ("auto-run").

You can press both of your mouse keys, hold them, then steer by moving the mouse.

I got the same problem. As soon as I longer press the w button the char will continue to walk even after I released the button. The problem was my rubber dom (the key itself). Because we are always pressing w down so hard and so much this key is under large pressure and the rubber is unable to refold itself fast enough. You can test this by using the left and right mouse key to move.