Could Seizures And Low Sodium Levels Be Due To Tegretol?

My husbands age is 50 now. He got fits(after his rememberance) in 1981 when he was physically very much tiered. He took treatment in sree chitra tirunal and was on tablet tegretol 200mg 1-1-1. It was recogonized as complex partial seizure. Later in 1982 he got attack again as he skipped these tablets for 3 to 4 days as he was taking some other tablets for fever. Again he consulted Sree chitra tirunal and was taking tablets 1-1-1 for all these years. There was no attack for past 33 years (taking tegretol 1-1-1 with out fail all these years) except sometimes some facial changes if he was stressed a lot.
But last week after a severs physical activity he had fit attack that day night.we consulted a neuro and after all tests he found that my husbands sodium level in blood is very low(126 only).( He is not having any other health issue). Hence the neuro told that its because of tegretol and asked to chnage the medicine from tegretol to keppra 750 mg two times a day withdrawing tegretol in a months period.

we are very much worried whether keppra will suit him etc.etc..as he was on tegretol all these years and was fit free to. please suggest. we are confused.

thanks