What could my MIL’s “unresponsive periods” be?

If it isn't causing any lasting problems for your mother (principally) or for the staff, I should leave well enough alone. There's only any point in investigations if they might lead to a potential improvement in care or treatment.

But I'm seconding KatieKate - the only thing I've ever seen myself that was comparable to this was in a younger man who was having a partial absence seizure - in his case his total (I do mean total) lack of response lasted about fifteen minutes, after which he got up and walked away oblivious of what had happened (which included that his dog had come to my house to get help; I am happy to report that dog and owner were later reunited by the police).

EEG's are not invasive or uncomfortable, so unless the doctors have already done one perhaps that might be worth asking about should this ever happen again?

In my opinion yes a sternal rub is appropriate when trying to rouse a unresponsive patient. The person applying the rub should be gentle while doing it & advance the pressure up in increments to get a response. (I’m a RN). Vital signs can be stable when doing the rub. A sternal rub will not cause any adverse physiological effects. I did it many times in my ICU days and used it when needed.

Sometimes there are miscommunications between the cardiac electrical system and the nervous system resulting in a person's body having trouble regulating their blood pressure and/or heart rate.  As a result, the blood pressure drops suddenly to 40/10 and the heart rate spikes to 140+ beats per minute.  This occurs for 2-4 seconds and is difficult to document on a EKG that is done even 1 minute afterwards.  Sometimes an episode of low blood pressure with irregular or rapid heart rate can be documented on a 24 continuous heart monitor.  A "Episode" or "Incident" heart monitor usually does not document the episode because the monitor has to be manually activated to record.  Tilt Table Tests are reliable in documenting this "miscommunication" between the cardiac system and the nervous system. 

The medical term is "neurocardiogenic hypotension and syncope (fainting)". 

It can take 5 to 30+ minutes for the person to regain consciousness and each episode might be different in length of and degree of unconsciousness.  Sometimes people regain consciousness but have difficulty responding to stimuli such as deep pressure over the sternum.  Also, sometimes the person is extremely tired after an episode and will sleep soundly for a few hours.

Another cause of unresponsiveness can be the irritation/stimulation of the Vagus nerve which results in low blood pressure and/or fainting.  A person can simulate the Vagus nerve while straining to have a BM, resulting in them passing out/fainting while on the toilet.

A cardiologist who specializes in heart arrhythmias might be able to correlate your Mom's unresponsive episodes with episodes of short-lived irregular heart rate or low blood pressure.

This has happened to us at least 4-6 times in the last 2 years.  We get mom awake enough to get out of bed and on the toilet then out to the front room for her meds and in her chair and she is out for most of the day.  We've taken her to the ER twice but everything comes back "okay".  Now we just keep her comfortable and let her sleep.  Then the next day she is back to her "normal".  The comment about mini strokes is interesting.  We believe she has had those and maybe these are the side effects of those?   She is in early advance stage.  I hate this disease!

My mom had something similar but hers was due to blood sugar fluctuations (though she is not diabetic). Only happened once but was very scary. She was inpatient at the time.

Thanks GardenArtist. MY MIL is 76 years old and has minimal medical needs besides the Alzheimer’s. At 6 AM she is given her thyroid medicine and blood pressure pill (she has been on those for years). She is not prescribed sleeping pills and goes to be around 9 each night.

This could be the “blacked out “ period after a seizure. My Mom was having petite mal seizures....the neurologist explained that the follow on black out period was usually longer than the duration of the seizure.

also...possibly mini strokes. Once that started happening to Mom...she would go a couple days of non responsiveness. I could not convince the docs to do another cat scan, because there was no treatment option so it made no difference if they could confirm or not. So, we never knew for sure.

Have you talked to a neurologist.

Specifically, what meds is she being given at 6 am?   And what time does she go to bed?  How old is she and what are her medical conditions?   Is she being given sleeping pills at night?

Someone here who's a nurse perhaps can address this question:  isn't deep pressure over the sternum performed on an unresponsive person when a cardiac episode is suspected?   But if her vitals were stable, would a sternum rub be appropriate?