I honestly would not open capsules and guess on how much you are taking. The capsules (in some cases) are there to carry that medication to a certain part of your stomach before being released. Therefore, I'd take your regular dose, and call the doctor for a proper tapering schedule (with new Rx's for 100mg pills to make this process easier).

Have you considered that your pain is 'letting up' because you are taking the Gabapentin?? That is what the medicine is supposed to do, after all. You may go through this process only to find out that your medicine was working and you have to restart it to get your relief back.