That you have epilepsy, that it is service connected, that it is now 40% are not likely to be relevant. The military already conceded that you have epilepsy and that it is service connected, as evidenced by the 10% severance. The fact that it has gotten worse and is now at 40% is a red herring. The VA covers the compensation for things that get worse. Military retirement, by law, can only look at the state it was at discharge. If any of your statements to the military include "got worse" or similar lines of evidence, you are arguing that your severance pay was correct. I don't think that's the argument you are wanting to make. You need to restrict your evidence to how it was at discharge. How often the seizures were with the medication you were taking at the time of discharge, not the day after discharge, month after discharge, or 4 years after discharge.
While it seems unfair that they don't consider the way your whole life has changed and the increased difficulties, the laws are written such that the military only gets to consider what your disabilities are like at the day of discharge and the VA is responsible for how things deteriorate from there.
Put in a claim for an increase to your rating with the VA. Likely you deserve higher compensation. Ensure the evidence you send to the PDBR supports the correct story that needs to be told. Likely you deserve a military retirement. Find a good VSO in your area, they are likely able to help sort out what evidence is good and for who.