Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand your concern for your fellow Leo because he seems to be less focused on food, lethargic, and you noticed him having twitches when he was sleeping last night and he is trembling this morning and seems sensitive to touch.
It is certainly possible with your description of twitching 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 mall 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.
There are several other things that can cause muscle contractions other than petite mal seizures. Infections, nerve damage or inflammation, toxin exposure, kidney disease and mineral (especially calcium) or electrolyte disturbances can all cause muscle fasciculations (spasms) as well.
I need to ask if you recently applied any topical flea medications or could he have been exposed to an insecticide? If so 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, lethargy and a decreased appetite in sensitive dogs.
Another possible cause of his symptoms is intervertebral disc disease. This is when the spongy discs between the vertebrae in his spine either prolapse or leak and put pressure on his 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.
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 should be seen by a veterinarian on an emergency basis today.
If his color is good and he is eating, drinking and behaving normally otherwise I suspect that he is stable but I do recommend that your veterinarian examine him and run some tests to determine why he is having these muscle spasms as soon as possible. I wouldn't wait too long to have him examined 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.
Please let me know if you have any further questions.