I went to change water tonight, and one of my Santa Cruz didn't "run and hide" like he usually does, I picked him up, lots of tongue flicking, but no attempt to flee and very lethargic?

I checked him over visually, seemed ok, but 'weak', I put him in a smaller container with water and some damp kitchen towel in case he was dehydrated, checked half an hour later and he was dead with his mouth open.

The others all seem fine?

This was the tank that I thought may have eaten a red wiggler the other week, but seemed ok afterwards.
The last two feeds have been ok, but the third feed back (a trout feed) and one of these three regurgitated. Again, I checked at the time and they all seemed fine.

I really thought it was the male because it was tiny compared to the other two (2 females and 1 male) but looking closely at the tail, I am pretty sure it was actually a female so has obviously had a growth issue.

I feed a mix of trout and pinkies, alternating both with worms less often at present as its so damn cold! And Dillies (smelt) when I can get it..(but not for a few months) Although he/she was small, she was definitely eating.

Anyway, the tank seems clean, the others seem healthy, shedding fine, very hungry,

Could the lob worms ( that were actually red wigglers I bought from the bait shop) have caused this several weeks later or is it likely to be something else? If something else, I would like to prevent it from happening again? or is it likely it was just a runt that got weaker and weaker?