Electrolyte imbalance with daily use of Osmotic Laxatives?

I have been using Lactitol Monohydrate, Osmotic Laxative, similar in action to Lactulose, daily for 7-8 months now.

I have IBS-C, I use it at night, to induce a morning bowel movement. It has been working quiet well.

Now what worries me is that, I haven't been drinking 6-8 Glasses of water. I only drink as needed, or mostly with meals. The warnings and precautions on the laxative leaflet says that if used for more than 6 months can cause electrolyte imbalance.

I have been using for more than 6 months, electrolyte imbalance and de-hydration can cause permanent brain damage, I have read. I want to know, what are the chances that it have caused brain damage?