It's simple. Pressure is a force, due to the change in Momentum when a particle bounces off a surface. Because it is a force, it is a vector, (it has a magnitude and a direction), like velocity or acceleration, not a scalar, like temperature or volume, or electric charge.
Secondly, the total pressure must remain constant (principle of conservation of momentum - Newton's third law). So when velocity increases, since the apparent direction of this pressure vector shifts in the direction of the motion, (it appears to align more with the flow motion), the component that is parallel with the motion (dynamic pressure) increases, and the component that is normal or perpendicular to the flow decreases. The total pressure (magnitude) hasn't changed. Only the components have changed due to a perceptual change in the vector's direction relative to the motion of the observation.
Once you understand this, many things make more sense. A common instrument for measuring Angle of attack these days is a pitot tube with two orifices. One points straight ahead and measures the pressure of the flow vector from that direction. The other is oriented 45 degrees downwards from the forward-oriented orifice and measures the pressure of the airflow vector at that angle. Comparing the two (with appropriate software), allows a computer to calculate the Angle of Attack.