It is dangerous because it points to an underlying issue like maybe an infection, stroke, electrolyte imbalance, etc. So if you miss the delirium and think they are just "getting older" or they are "just having a bad day" or that it is "just dementia progressing" then you could miss the underlying issue and the patient could die from it. So to deal with it you need to diagnose it and then do a workup to find out what might be going on and fix that problem if possible.
