You should talk to your loved one’s doctor about the constipation and see if there is a way to prevent this situation rather than have to react to it. This can be very difficult to deal with.
As far as his aggressive behavior, you might want to check out the suggestions on helpforalzheimersfamilies.com and see if any of these are helpful.
If you aren’t able to manage your loved one’s aggression using techniques such as removing the thing that is bothering him, redirection, taking the blame, etc. then you may need to talk to his or her doctor about medication that will help this person feel less agitated.
Learning new ways to interact with your loved one are likely to be very helpful.