Question regarding my spaceship.Follow

I've been playing for 4 months, and I've never had this problem before last night.

I'm in my ship and I set my speed for maximum power. When I hit the Alt key, it lets me move my mouse around the screen like normal. No problem. Now, when I hit Alt again, instead of my ship changing direction according to mouse movement, I change the direction I'm looking. I continue to fly forward, but I can look up at the roof and floor of my ship while flying. Is there a simple fix to this? Thank you in advance.

If you have a joystick connected.....this can happen as well. I use a joystick to fly....not mouse and keyboard. When I press the alt key I get free mouse, when I press it again.....I can loook around, but to change direction...I have use the joystick. That also may be in your options it may be under MISC or Interface buttons. After the update they just did on Tues....alot of my setting reset themselves to default. This might have happened to you too.