Why is my senior Corgi suddenly anxious, shaking, and acting distant?

Sounds like Kaden has a pretty significant anxiety disorder. I suggest you speak to your vet about what treatments are available. Often times older dogs will change and start exhibiting behavior like this when their eyesight and/or hearing starts to get poor. That may be the problem. I don't know. You can refer this article for some options to help anxiety but it seems like the prescription medications work best. ( https://www.petcoach.co/article/7-natural-treatments-for-dog-anxiety/ ) The bump on the leg is hard to see but it looks like it may be a lick granuloma. He could be licking that area because the underlying bone is hurting him or it could be from the anxiety. ( https://www.petcoach.co/dog/condition/acral-lick-dermatitis/ )

Ruling out an underlying health issue such as pain or illness is always a good first step when your pet experiences a sudden behavior change. As seven is the start of the senior years, it is possible there is some pain from laying in the bed, or arthritis causing problems. if Milou checks out health, trying to find if there is a pattern to the "attacks" may be helpful- does it happen the same time every night? Same spot? Same triggers? Is the neighbor arriving home in a noisy car at that time, etc? This may help you figure out what is triggering it so you can make some adjustments- IE moving the bed somewhere quieter, making sure your dog is fast asleep prior to that time, getting out excess energy before bed, feeding a treat to keep the stomach from becoming too empty and causing growling/discomfort, etc. If you can't seem to find any pattern at all, taking a video of the even to bring to your vet or a local trainer may be helpful in better identifying what is going on, and finding a solution.

Shaking is usually a sign of pain, It could be related to the disc herniation, it could be something totally different, it's very hard to know without checking him. I would recommend taking him to the vet ASAP, this is obviously not a normal behaviour and this needs to be investigated and treated quickly.

That is concerning. It is possible there is something they are hearing outside, such as a neighbor or wild animal, or even a critter in the walls that could be bothering them. Looking for a pattern (time of day, certain TV or radio shows on, person coming home, etc) may help you figure out what the trigger is to stop the behavior from happening. Taking a video of the behavior and bringing it to a trainer or behaviorist may also be a good idea to see if they can pick out any details that may provide more information.

I'm wondering if Lobo could have a prostate problem causing him pain, as those can be common in unneutered dogs. He certainly sounds uncomfortable, so I'd have him checked out by a vet in the morning.

Sounds like Kringle is in some level of distress. Whether or not it is manifesting from pain or true cardiopulmonary pathology is unclear. He should be taken into your veterinarian and examined soon. If you feel he is having any difficulty breathing, which generally does sound like the description you are offering, he should be seen on an emergency basis. The doctors will want to x-ray the chest to assess the presence of a respiratory infection, or a primary cardiovascular/cardiopulmonary disease process. Hope this makes sense.

Poor Gibson! As dogs age, they can develop canine cognitive dysfunction (similar to dementia in humans) or decreases in their hearing and sight, which can result in anxiety and behavioral changes. Restlessness, panting and sudden jumping could also be a sign of pain. At this point, your best bet is to take Gibson to his vet for evaluation to determine if he has any apparent sources of pain, which could be managed with pain medication. If not, your vet will be able to discuss some of the different medication options to try to manage cognitive dysfunction, but these are not always overly effective. I hope that all goes well!