I'm thinking here of both UK and US law, which I assume will differ.
Suppose a defendant in a civil case (type of case unspecified) would ordinarily have no defence against the plaintiff/claimant's claim, and would be ruled against in damages for a large sum. The defendant had a confirmed mental health condition (also of unspecified type) which is agreed overwhelmingly likely to have been a (or the) cause of whatever action(s) gave rise to the case.
In what circumstances and to what extent will this change the ruling, or the amount ruled against them, in US or UK law?
Some examples, although I'm really after general principles, these just illustrate the situation. (In each case assume the incident was unexpected and either no other person helps/cares for them, or any such people could not reasonably have foreseen/prevented it and would not be liable). I haven't numbered these because I'm really looking for principles and generalities rather than answers to these hypothetical examples:
- Person has "walking insomnia". While sleepwalking one night they commit an act against a person or property which would usually result in a valid civil claim for damages.
- Person has trauma and cannot always control their reactions when it is triggered; they run out of a shop when something triggers it and knock over numerous people and displayed products/shop fittings.
- Person has cancer in part of their brain that controls self regulation. Nothing happens until one day they attack somebody, an act for which they have no prior history, and agreed to be due to their medical condition.
- Ditto but the issue is a congenital or regenerative neurological condition, and their family do not knew or cannot react in time to prevent an actionable incident.
- Person has ADHD (ADD) or OCD, and is functional in society but medically it is agreed they will never have good or even usual control of attention wandering or forgetfulness or compulsive behaviours, there simply is no way to gain this. Damage results.
- A reluctant parent with a bad parent-child relationship hears a rumour on the internet that mental health is no defence against civil damage claims, and decides to sue their offspring for massive damage caused to their house on the night of their 18th birthday. Because of the stress they had also not recognised their parents who arrived, and believing themselves attacked by strangers, slashed at them with a knife in panic, causing life-changing injury. Their condition had never remotely been like this before and there was no realistic way to anticipate it might happen, nor any incident previously requiring precautions. Conveniently on that day the youngster also inherited the kind of sum that would be needed to pay any damages if the claim were successful.