I want to help you with your boy's problems, but I will need a little more information:
How long has this been going on?
Has he had a history of problems like this?
Does he have a head tilt? Is he circling?
Are there behavior changes?
Let me know this information and I will respond with further thoughts as soon as possible!
He started tripping about a month ago while out walking but has not had a history other than that. He has been a health dog with very few problems. He does not have a head tilt, but there is a small lump on his neck that feels like a tick but it has been there for about a year. He seems fine between episodes of dizziness.
So, these are truly episodes of dizziness and shaking? Does he only vomit during the episodes?
I will assume, for the sake of getting you some thoughts and ideas sooner, that they are true episodes and that he is normal between with no vomiting...
I have a couple of concerns in this instance:
With the tripping that you describe, I would be concerned about something affecting his neurologic system. If that's the case, he could be having some simple or complex seizure activity during these episodes that then resolves.
This sort of diagnosis isn't easy to come by and your veterinarian would likely discuss with you options of testing with blood work first, followed by possible CT scans and fluid taps at the most aggressive. If seizures, though, can be suspected, your vet might also talk with you about the option of trial treating after ruling out the other things I will mention...
In some digs, cardiac arrhythmias (or abnormal heartbeats) can cause episodes of weakness and dizziness from low blood pressure. This can be tested for relatively easily by looking at blood pressures and EKGs.
The other concerns become more metabolic problems. Does he have kidney problems? Could he be getting a low blood sugar at these times?
As you can see, there are many things that can cause such episodes (and my list is in no way exhaustive!), and unfortunately they all require some sort of testing. I would recommend that you get your boy in with your veterinarian to look into some of these tests.
As always, if you have further questions, please don't hesitate to ask them!