When people have Alzheimer's disease, they can develop delirium easily. Delirium is a temporary change in consciousness which can cause delusions and worsening confusion. Dehydration can cause delirium for sure,
so if he was truly dehydrated, this may have caused your husband's symptoms. However, in my experience, dehydration usually causes low blood pressure, and usually the person is too dry to develop sweat. So, before you make assumptions that is was just dehydration, I would have him see his health care professional. The episode you describe to me almost sounds like something we call presyncope, which is where a person gets pale, sweaty, and almost faints. This can be caused by dehydration, but it also can be caused by anemia, heart problems, or constipation. I would feel better that he got this checked out. I should also mention that some Alzheimer's medications can slow down the heart rate and cause syncope, so I want you to be sure this is not happening to your husband. Good luck!