I had weakness in my legs in some seconds this night, and had problems to breathing when this was going on. dangerous?

See your doctor: I'm not sure what is going on but these are concerning symptoms and you should see your doctor for an exam and testing to be sure it isn't serious.

Need to see a MD: based on what you described it would be impossible to make a diagnosis. I be concerned about the difficulty breathing and you should check with your primary care provider otherwise go to the emergency room to be evaluated

Vague symptoms: Your symptoms are vague. It sounds like you may have pinched a nerve in your legs leading to a short temporary weakness from which you got anxious. If this returns or persists, you need to see your doctor for a physical exam and evaluation. I would not worry and this does not sound dangerous as long as it does not recur.