My elderly sheltie has recently developed a problem with seizures. I can't be sure but I think it may be related to the Nexgard product I was giving him monthly for fleas. I have had him off the Nexgard for several months and just recently noticed a few fleas on him. It seems like all of the chemical drugs/insecticides can cause seizures and neurological problems whether they are given oral, topically, or from wearing a flea collar. Can anyone suggest a product that will not make his seizure problem worse? Or is least likely to lower the seizure threshold? I have also read about other products including diatomaceous earth and herbal sprays but do they really work? One of my other shelties had an adverse reaction to Trifexis so I am reluctant to give these insecticidal once a month treatments. Any suggestions would be appreciated.