I understand your concern for your fellow because you are noticing him having facial tremors, drooling, and foaming which last for 1-3 minutes with 20 minutes between episodes.
Are these episodes of his head bobbing, or are they small groups of muscles twitching on his face/head?
Can he control and stop these episodes if you distract him (talk to him, offer him a treat)?
Do these seem to happen more when he is trying to do something (intention tremors) or more when he is at rest and relaxing (resting tremor)?
If these tremors seem to be muscle spasms of a group of muscles that he cannot control or stop it is certainly possible that your fellow is having petit mal seizures. These seizures affect a small group of muscles in a particular area of the body. They are not of the same significance as grand mal seizures (loss of consciousness, whole body, rhythmic, uncontrollable muscle contractions with possible loss of urine and stool continence) because the chance of body temperature increasing and subsequent brain damage is much less. We cannot distract a dog and get these muscle twitches to stop, they seem to stop and start of their own accord.
There are several things that can cause muscle contractions other than petite mal seizures. Infections, nerve damage or inflammation, kidney disease and mineral (especially calcium) or electrolyte disturbances can all cause muscle fasiculations (spasms) as well. None of these can be consciously stopped by your pup.
There are also benign head tremors which we can see in some breeds of dogs, Bulldogs being one of those breeds. These are poorly understood but tend to occur when the dog is awake but relaxed. They can involve up and down "nodding" type movements or side to side "saying no" type movements rather than muscle spasms like we see with petit mal seizures. They will stop if the dog is distracted by something else. Very rarely these can signify brain disease, but in most instances they are benign and do not bother the dog. Although he is a Bulldog the episodes you are describing don't seem like these because your fellow's episodes seem more like facial muscle twitches and head bobbing episodes don't usually involve drooling.
I need to ask if you recently applied any topical flea medications or could he have been exposed to an insecticide? If so this can be a reaction to a toxin and you want to bathe him thoroughly to remove as much of the toxin as possible with something like Dawn dishwashing soap and cool water. Do not use hot water or scrub his skin as that will increase toxin absorption. Some flea control products, especially the over the counter products with high amounts of pyrethrin type insecticides can cause muscle twitches in sensitive dogs.
Another possible, but unlikely, cause of his symptoms is intervertebral disc disease. This is when the spongy discs between the vertebrae in her spine either prolapse or leak and put pressure on her spinal cord. This is quite painful and can lead to painful muscle spasms or if there is enough pressure then even paralysis can result. Keeping him very quiet, no running, jumping or bending over (elevate his food and water bowls to head height) is best. This is more commonly a cause of muscle twitches along the back or neck rather than head tremors, but I mention it to be complete.
If he seems to be progressing in symptoms and has a grand mal seizure (unconscious, unaware of surroundings, repetitive, uncontrollable whole body muscle movements with or without loss of urine or stool) then he definitely should be seen by a veterinarian on an emergency basis today.
In most cases with focal tremors or twitches we don't consider them an emergency, but given that his have been repetitive today and aren't stopping I think an emergency visit is best.
The veterinarian at the emergency clinic can examine him and run some tests to determine why he is having these motions and make sure that they are benign. I wouldn't wait too long to have him seen as some of the things that can cause muscle spasms (like toxins, electrolyte or mineral imbalances) can cause long term problems for your fellow and may be indicative of serious diseases. If this is intervertebral disc disease it is very important to relieve the inflammation so it does not progress to paralysis. If this is secondary to high blood calcium levels then addressing that promptly so there is no organ damage and tissue calcification is best.
It will be very helpful for the veterinarian to see one of these episodes. If you can tape one of these episodes on your cell phone and take it in so they can see it then that would be very helpful.
Please let me know if you have any further questions.