If it don't fit- don't force it has to be among the most understated and often ignored warnings. I've lost count of the times that I have gone beyond ignoring into limit pushing :} But- some risks are..more.
Warnings about SHOCK and Hypothermia do indeed apply to stupidly large cold enemas and if retained more than moments.,
You risk depressing your core body temp below what's safe. It's like any other risk factors. Roll a 20 enough times and your number comes up. Some things are a roll three times. Yeah, the simple bodily protection routines of - this hurts too much- tend to mitigate our self-abusive tendencies. Even wanting to please our lovers etc, has a chance of raising our pain threshold, but not easily into the Hypothermia zone unless we;re of small mass+ large volume/very cold enema. From that- a retention "whatever" might be not smart. It's all about realistic evaluation of dangerous or not.
Which does NOT mean that there's only a small risk- just that there's more than a few factors at work.
Psychological dangers too. A cold enema can *HURT* so badly that it's arguably into the mind twisting zone for some of us. Again, we're all different in our comfort-or discomfort- thresholds for what's boringly painless and what's mortal shock trauma PAIN. Anyone here remember the Sybil story?
Play safe,consensual, and do your homework on risks FIRST so I can enjoy chatting with you a long time.