That means you aren't getting 10mg anymore. The peak periods of the med will be too far apart to overlap resulting in a peak of over 5mg now as opposed to 10mg if you took the 10mg in the same sitting.
However the way you are taking it, which is unconventional for a SSRI, will result in a top up effect that prevents the med dropping as low as it would if you were taking 5mg once a day.
So, perhaps you were on too much? Or perhaps you started increasing the dosage too quickly making the side effects much more intense?