I love Danes. Always wanted to own one but would never put myself through the torture because I know they have a lot of health problems. Their average life span is only 9 years or so. You mom is doing a good thing to keep him calm because they also suffer from bloat.
Im not a vet but I have heard that seizures are common in most old aged dogs. Sometimes you will need to try several different meds until you find one that actually helps. However, unless the seizures are constant (at least once a month) the vet might decide that meds are not necessary. Again I am not a vet and am only telling you what I have research myself when I have had similar issues with my pets. Hypoglycemia is also makes dogs have seizure like symptoms so your mom can get him checked for that.