There are so many different forms of myoclonus and they can be caused by so many different things that it's quite difficult to hazard a guess as to what could be causing this in your girl. There are a few breeds (labradors and dalmatians mainly) who are genetically predisposed to myoclonus but there is another form that can be caused by medication. Are the two types of medication you have mentioned the only things she is taking or has taken? Since you say she was having spasms before the CHF it's not likely that it has anything to do with the meds you are giving her for that. Have you had her for her whole life? Or was she older when you got her? Myoclonus can also happen as a result of the dog having had distemper. Do you know if she ever had that at any point in her life?
Falling asleep is the classic time for myoclonic jerks to occur. Even people with perfectly normal nervous systems can have myoclonic jerks while they are falling asleep. If you have ever been juuuuuust aboutu asleep, only to jump awake because you feel like you are falling - that's a myoclonic jerk. It's a completely involuntary muscle movement that you have absolutely no control over.
What type of food have you fed her during her life? I know that right now you are feeding her the Hills geriatric diet, but before that, when she was young and healthy, what were you feeding her? I am asking because there is something called serotonin syndrome that can result when a dog's body converts the proteins in their food into something called 5-hydroxytryptophan that can cause myoclonus in dogs.
The problem is, once a dog HAS myoclonus, it can't really be cured, but it CAN be gotten into remission. The fact that you said that she can trigger these myoclonic seizures by bending down to drink. Hiccups is actually a form of myoclonus, and hiccups can be triggered by pressure on the vagus nerve. It's possible that she's putting pressure on the vagus nerve when she bends down to drink and that's what is triggering the seizures. At this point, managing the condition is the only thing you can really do. Can you try putting her food and water bowls up on a stand so that she doesn't have to bend down to get to them? I know that dogs sniff at EVERYTHING, it's how they get information, so it's likely that she will continue to bend her head down to sniff at whatever she needs to sniff at, but if you can make things as easy for her as you can and prevent her from having to do any unnecessary bending that MIGHT help a bit.
This is just such a tough problem. My heart goes out to you. Nothing is more frustrating than having one of our beloved family members suffering with something and not knowing what to do to help them. I will do a bit of research and see if there is anything that is suggested to alleviate the seizures.
Thank you so much for your response. We got Ginger at age 6 months from the Humane Society. She was sprayed and vaccinated at that time. I keep up with vaccinations and heart worm preventative and sometimes Frontline. She has eaten Purina One dry dog food most of her life. I doubt she ever had distemper. She takes prednisone in August when itching makes her very uncomfortable. I wonder if her congestive heart failure is causing pressure on a nerve. Her heart is enlarged and she is becoming barrel chested.
I raised her dish yesterday. I tried before, but I have a better surface to raise in on this time.