Seizures are common in dogs. Idiopathic epilepsy usually is first diagnosed between 4-8 years of age. This would be the most common cause of seizures in your 6 year old.
A diagnostic work up on a dog that has started seizing include a complete blood count, blood chemistry scan, urinalysis and fecal analysis. This rules out other common causes of seizures.
Treatment for seizures depends on how often they occur and how bad they are. If they are infrequent (1-2 a month), last only a few minutes and occur singly (not several at a time or in a day), they are often not treated. If they occur more often or are more severe, they are treated. The drugs most often used are valium, potassium bromide and phenobarbital.
Owners should keep a record including date/time, length of the seizure and any other observations that they think might be important.
You do not need to use cold to shock him. It will not shorten the seizure. Benadryl is not effective either and as you noticed, he can not swallow during a seizure.
Let me know if you have followup questions. I'll be online for a short time longer tonight and back on tomorrow.