I'm hesitant to post as I've never had to deal with such issues. A couple of things do come to mind, however.
You are in a wait and see mode right now waiting on results. It seems like a big coincidence that the symptoms arose only a day after giving the Sentinel. It may be that, a liver or neurological issue or a combination of any of these.
One thing I was wondering is if milk thistle could be given to de-toxify the liver. If it is either LS or a reaction to the Sentinel, it would seem to be something that could be done and you might see some positive results. I found this info....
"Milk thistle protects the liver against drugs and heavy metals. It also activates protein synthesis. If liver cells are dead or damaged due to illness or toxic exposure, milk thistle will activate the growth of new cells. Liver issues that can be treated with milk thistle include hepatitis, cholangitis, pericholangitis and hepatic lipidosis.
Other uses for milk thistle are as an anti-oxidant and anti-inflammatory supplement. It can also be used to treat gallstones and inflammatory bowel disease.
Milk thistle taken after a drug regime may protect your dog's liver against damage from chemicals. This can include chemicals taken for treatment of illness or even vaccinations or heartworm, tick and flea preventative applications."
From this source....
Milk Thistle Dose for Dogs | DailyPuppy.com
I am not advising this but do think it is something you could consult with your vet about since this *could* be a reaction to the sentinel (please note the disclaimer). Maybe someone with some experience with this could offer an opinion?