Most of your symptoms are common with a number of conditions. Then you said:
* Strong bitter metallic (yet occasionally intensely sweet) taste (mostly on the left side of the mouth) as well as ringing in ears serves as precursors to severity of the symptoms. The more bitter (or rather caustic, almost like sucking on a battery) the taste, the more intense the ringing the more severe the whole group of symptoms for the next several days or weeks will be.
Metallic taste narrows things down quite a bit since there are not many things that can cause a metallic taste. Usually this is bleeding in the mouth, heavy metals or certain medications. The "sweet" taste further narrows this down. Up until this comment I was thinking along the lines of arsenic, which is common in the water system of some parts of the country and is a cumulative poison. But this has a garlicky taste. You said sweet though and lead has a sweet taste. In the Roman days they would use lead containers to store wine in to impart a sweet taste.
I would start by having your serum lead levels checked. Common sources of lead poisoning is from lead plumbing pipes in old houses, old leaded paint and lead contaminated soil.
If lead levels are high then the easiest way to remove the lead is with silica sources. Silica displaces and binds lead to remove it from the body. I prefer using food grade diatomaceous earth for a silica source. Taking amla berry when removing metals will help protect the DNA from the heavy metals as they are removed.