Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear about your fellow's episode of collapse onto his side, and stiffness. When a dog seems to collapse like your fellow, and then come around and seem pretty normal we worry about 2 things.
1) A seizure which is a loss of conscious muscle control with rhythmic muscle contractions occurring. These dogs may lose urine or stool continence, they are unaware of their surroundings and their muscles tend to be very tense during the episode.They seem fine afterwards though puzzled about what happened and can be a little tired. This is a link to a video of a dog having a seizure: http://www.youtube.com/watch?v=VSL1_yeKo5o&feature=fvwrel
2) the second possibility is a fainting episode (syncope) which can be caused an irregular heart rhythm (either very fast or very slow) such that oxygen doesn't get to the brain and they pass out. These dogs seem to stiffen and then slide to the ground like a wet noodle and have more relaxed muscles. These dogs don't display the typical rhythmic, large muscle movement like with a seizure. They too tend to lose consciousness, the heart resets itself and they "wake up" and seem normal. Some of these dogs lose urine and stool continence and some do not. They may have minor muscle twitches due to low oxygen levels, but they are not as stiff or rhythmic as true seizures. This is a link to a video of a dog having a quick syncopal episodes. They are usually longer then this dog's: http://www.youtube.com/watch?v=mkj4jREIec8&feature=fvwrel
The irregular heart rhythm that leads to syncope can be hard to pick up on a regular exam as they may be triggered by exercise or excitement or even sleep (extreme relaxation). And if they aren't stressed at their exam their heart rate may be slow and normal (these are dogs with tachycardia or fast rate arrhythmias) or if they are stressed then their heart rate may increase to an normal level (these are dogs with bradycardia or very slow heart rates).
Both of these "episodes" can be triggered by excitement. If your fellow has a history of a heart murmur or heart disease then a syncopal episode is more likely than a seizure.
Seizures in dogs older than 6 years of age usually signify that there is a medical problem. Younger dogs (6 months to 6 years) are more likely to be diagnosed with idiopathic epilepsy or seizures of unknown origin but in older dogs seizures are usually related to metabolic organ disease such that waste products build up and affect brain function or a primary brain problem (inflammation or tumors).
Unfortunately other than keeping him quiet there isn't much you can do at home. He needs a physical examination, bloodwork and possibly further testing to diagnose his condition.
If this is heart disease we need to properly diagnose his arrhythmia to know how to treat him medically and if this is indeed a seizure then looking for and treating underlying metabolic organ disease is needed or medication to help decrease seizure frequency and severity if this is related to primary brain disease.
If you could videotape him (many cell phones have the capability to do this) that would be tremendously helpful for your veterinarian as well.
Please let me know if you have any further questions.