Dogs sense energy. Most will recognize that their person does not feel well long before the person does. Dogs will recognize when their owner is afraid or anxious.
You will see this a lot when teaching basic dog training classes and in dealing with dogs that have behavior issues.
Not all of course, but a large amount of the time it seems that dogs exhibiting certain behavior at a dog class can be traced right up the leash or lead attached to the dog's owner.

An example: When you have a dog owner that feel anxious and is expecting a problem when another dog approaches their space, this energy is picked up by the owner's dog. The anxious dog owner will have a dog that recognizes that the owner is upset and anxious and will immediately behave differently. The dog will feel that something about the situation, what ever it is, is "bad" because the of the owner's reaction.
Seen many, many examples. Dogs pick up on energy and how you feel.

Sometimes, well most of the time, it is harder to train the pet owners than it is the dogs.

Mac

2 months later than this picture I was diagnosed with colorectal cancer,
She knew before I did!

several years ago I attended an inservice training at work where a man and his therapy dog spoke... His family was in the medical field and he volunteered at the local hospital with his dog, and the dog had a "gift" of sorts. It assisted in identifying patients hospitalized with unknown illnesses. I don't recall the entire story anymore but they would gain permission to take the dog into the hospital room, and the dog would climb onto the bed with the patient and lie next to them, and after a while certain parts of the dog would get warm- that coincided with where the illness was in the human counterpart. It took his expertise of knowing the dog's anatomy, but they visited the area hospital on a semi-regular basis until the dog passed. Hearing that testimony, and knowing the nature of my own animals, I believe they have ways of telling us when we aren't well.

I am an epileptic as well as have extreme blood sugar fluctuations (due to seizure medication). My lab knows when things are fixing to happen. He will stay very close to my side and whine beforehand.

I had that same back issue in 2015. I am not a fan of surgery but it hurt so much anything was better. Had the micro discectomy. Walked out of the hospital 4 hours later. 100% better. Wish you the best. I was 54 when I had that done

Listen to Doc, Gary!

Dogs can smell or sense organic compounds in parts per trillion, including chemicals in your system that indicate impending seizures, cancer, high blood pressure, all kinds of things! They have amazing sniffers paired with their ties to humans they care about. It's a powerful combination!

Please let us know how this turns out. All our best to you!
Patrice