When the membrane potential is decreasing towards the resting potential, the Na+ channels are most likely to be in their inactivated state (C in the given image).
A is resting stage
B is activated state
C is inactivated state
The conformational change that flips the inactivation gate to the closed state is a slower process than the conformational change that opens the activation gate. Therefore, after the sodium channel has remained open for a few 10,000ths of a second, the inactivation gate closes and sodium ions no longer can pour to the inside of the membrane