Sorry to hear of the situation. Do you think he was becoming depressed again prior to the argument?
Ok, thanks for the extra information.
Whenever we encounter the possibility of suicidal thought or intent we approach the matter directly and I see no reason why you shouldn't do the same right now. If I understand your posts correctly you are concerned about the possibility of Depression and/or suicidal thought and so I'll make some suggestions for both possibilities:
In regards XXXXX XXXXX with the possibility of him feeling suicidal you should ask him directly whether he is feeling suicidal or not. Tell him that you understand that he doesn't wish to speak with you right now but that you need him to guarantee his safety at the moment or you will need to contact health services immediately. If he is unable to guarantee his safety then you should contact emergency mental health services ans explain the situation (they will advise you on how to proceed).
If he can guarantee his safety then there probably isn't an urgent need for action. People who suffer from Depression often have trouble with a particular symptom called rumination. Rumination is a repetitive cognitive process that involves a person repeatedly engaging in negative thoughts and this is often noticeable by them sitting quietly for extended periods looking distressed (I think this may be what you are seeing). Rumination can certainly drive mood further down and so while he may not be in any current danger I wouldn't want him to stay ruminating for too long (more than 24hrs).
When he previously developed Depression did he receive any form of treatment? If so, what kind?
If he can guarantee his safety but he continues to appear to be in a distressed state after 24hrs then get him to contact his previous doctor for a review (or contact his doctor yourself). If you feel at any stage that he may be at risk then contact emergency services and ask for advice on how to proceed (this varies from country to country).
Antidepressant medication forms only part of the recommended treatment for Depression and he should also have been receiving Cognitive Behavioral Therapy (CBT). Older males often aren't to keen on the idea of psychotherapy so he may find a good CBT based self-help program useful like this one here.
Depression can be difficult to manage and it is more than a family member should be burdened with handling. I encourage you to get other people involved (preferably a professional) so that your not forced to try and make difficult decisions.
I hope this has been of some help. Please let me know if you have further questions or would like me to clarify any part of my answer.
Sorry, didn't see your other post before I answered.
If he is taking pain killers then this potentially changes the situation entirely. Yes painkillers can have a sedating effect and he should be assessed by a medical doctor as soon as possible to discount the possibility that he is over medicated.
Contact an emergency medical line straight away and ask for their advise on how best to proceed. If he is experiencing cognitive impairment from over medication this would warrant an emergency call.
Dehydration can have a marked impact upon the effects of medications and it may just be that he is dehydrated and as a result over medicated. If you are away from home (and have travel insurance) then I would suggest you take him in to the emergency ward of the nearest large hospital.
Best of luck.
If he is in a state where he can't or won't recognize that his family believe he needs to be assessed (and there is the possibility of a medication complication) then you may need to check whether there is a doctor who can come to you. If you happen to be staying in a large hotel or resort you can often have the concierge/staff organize a doctor to visit.
Unfortunately there is no magic trick for getting a person to a medical assessment and if there is potential over sedation or cognitive disruption you may actually be wasting your time trying to produce any kind of convincing argument as he may not be able to respond properly. It is usually easier to convince a person if there is multiple people in the room so if you are traveling with other family or friends get them all together in the room and insist.