Hello again. I feel like I spend too much time in this section.
My two Black-necked Garters have very suddenly developed severe neurological problems. They don't have control of their bodies at all. They are moving slowly with their necks arched backwards, twisting as they move. Their breathing is heavily exaggerated and slow, and they go from rigid to limp to rigid. This is very sudden, within the last few hours. They weren't showing these symptoms this morning, or when I fed them on Monday. This is very similar to what happened to my sick female, but she had a fungal infection that we thought was the cause of it (though it had visually cleared up before she died). At this point, since I've gone through these signs before, I know they are going to die, probably tonight. However, I'd really like to know what is going on.

About them:
Both wild caught in spring/early summer. One male, one female. 20 long tank with about a third of it sealed and partitioned with water and the rest of it dry land. Substrate is a coconut fiber blend mixed with moss. Temps- 75 at night, ambient 80 in the day with a hot spot of 85+ (they are from here in Arizona). Eating silversides 1-2 times a week depending on how active they are and how much they are eating.
Their whole setup is practically identical to my Nerodia, but she's doing just fine. They haven't been exposed to anything new, their routine hasn't been changed recently, they've been on the same frozen bag of fish for a couple months now... I just don't understand how this came out of nowhere. We have 6 other snakes, so I'd really like to try to pinpoint this and avoid a repeat with anyone else... Any suggestions would be great.