One we see in the ER all the time.

Unfortunately in these circumstances the bar needed to take away someone's right to make medical decisions for themselves (including refusal of treatment) is quite high.

The best thing is to try to get him to go to the ER on his own. If he will not and you have already called the police (which you state you did), take away all knives, all guns, etc. And watch. Don't let him be alone. If he again worsens or makes threats, call the police again.