My husband, 88 yrs, dementia like symptoms.

My husband is started to have episodes lasting sometimes more than an hour where he goes inside himself. He sits there, eyes closed, mumbling & sometimes moving his hands & fingers like he’s typing. He’s not responsive to my voice & I have to shake him & talk loudly to get him to see me. Then he retreats again. I don’t know what to do except to watch him to make sure he’s safe. This is new to me & I have some memory problems myself.