When I suddenly stand up from sitting down, lying down, or suddenly start walking when standing still or even suddenly moving from a resting position, my face, fingers and toes muscles will tense up and feels a bit weak too.

Thinking too much about it will cause it to occur more. Playing games like captain's ball ensures that problem doesn't occur only during that game (better blood circulation? mental problem? <- can't think about it during game)

Please help! Please help! It's wrecking my life :(