Poor guy. I can understand why you are worried.
First off, I want to say, my family and I have seven dogs currently and have had other dogs in the past. We have had our fair share of dogs with anxiety, seizures, and just a lot of energy. All of these things can cause issues in dogs, but so can chemicals, neurological issues, and other such things.
I'm sure you have looked into many different causes, but sometimes it can be an unexpected reason. Do they happen around the same time? Do they happen around the same person? Could it be an animal or person in a near-by house or in the yard such as a cat, hawk, or fox?
Check your dogs food. Some foods can cause reactions, especially those with a lot of additives.
You mentioned the water. Flouride can cause serious neurological damage and some countries are trying to stop its use in water. However, until that happens you could try using bottled water. We buy reverse-osmosis water for very cheap locally. We fill up our bottles with fresh, clean water and it costs less then many other alternatives for a better quality product. We also use our well-water, however, it is very high in certain minerals and so not safe to use as an only water source.
Check to see if you are using any strong soaps, detergents, perfumes, or other spray or scent chemicals in the house. This can cause neurological and behavioral issues in animals, so watch for this. If the yard is sprayed it could also be causing neurological issues.
Look into any flea medication you are using. Some dogs may be more likely to react to parasite medication then others. Could it be connected with this?
Next, look into breed history. Our Cockapoo has mild epilepsy that effects her only one or two times a month at most, and always at night. It helps to keep track of (perhaps writing down) the severity of the episodes, possible triggers, when it was, where it was, and who was home at the time it happened.
Both Poodles and Cocker Spaniels are prone to certain health issues, and this seems to include anxiety.
Anxiety in dogs can be very extreme and sometimes easy to diagnosis as something else. Our poodle mix, Cedar, began to get very similar sound episodes after his "father" Arby, an older dog, passed away. We thought he was having seizures and even brought him to the vet for it, where they were unsure of the cause.
Cedar would begin to run around like something were chasing him (similar to Esther's seizures), shake like he was going to fall apart, curl up in a ball, hide in a corner, walk side ways, jerk, and his heart rate and breathing were worse. He developed a tic, was afraid to go outside on his own, and generally acted up during times when we were excited, such as when we first came home or something similar to that.
The way you mentioned that when you took him away from the house he didn't show it makes me think something in the house is trigger the anxiety. Cedar got over his anxiety slowly, over a few months, with plenty of exercise, the calmness of the other dogs, and realizing that when we cooed and fussed over him it made him more prone to doing it. Instead, we would calmly talk to him, say high, and get him up and moving and distracting his mind. Walks were especially important to getting nervous energy out.
I did want to mention seizures again, just because they can come in a variety of forms. Usually it includes shaking, but one of our dogs we were pet-sitting, Cleo, had a very bad seizure and afterwards went slightly delusional. She ran outside, barking at us like we were strangers, somehow escaped the fence and ran away for over a weak, terrified of anything she saw. When she came back she was okay, but the family had mentioned she had been acting strange a few months before it happened. Seizures can lead to odd behaviors.
Seizures can be due to the breeds genetics, the shape of their head (small skulls can lead to brain issues), and seizures can also be caused by chemicals, poisonous plants, and medications.
Lastly I wanted to say that Low-blood Sugar, something common in small poodles, can lead to all sorts of odd behaviors from anxiety to seizures, sluggishness, throwing up, and more. Make sure you dog is getting enough meals, even if they are small, to prevent this issue. Sometimes three or four small meals is better then two larger ones.
I certainly hope this helps with at least giving you some ideas of what could be wrong with your dog. Again, make sure to keep track of when and how bad these episodes are to see if there is a trigger or pattern.
Best of luck!