Dad getting very sick in waves, what is happening?

Im hoping my dad’s symptoms sound familiar to someone, or any suggestions to what might be happening.

Background:

• 91M, congestive heart failure, on a smorgasbord of the usual meds for his age.
• he can get around with a walker, but doesn’t move much. Has an aging mind, but not dementia.
• he fell 11 days ago. A few bruises, and he wrenched his shoulder. He can’t lay down because the shoulder hurts, so he sleeps in the recliner.
• taking Tylenol and Tylenol PM for the pain. I was worried about the PM, so I told mom to try regular Tylenol tonight.

New problem: He’s been having waves of feeling horribly sick: extremely weak, shaky, can’t catch breath, dizzy, disoriented, so tired he can hardly open his eyes, even feeling nauseous from the discomfort. The episode lasts less than an hour, then he’s okay again! He had 3 bad episodes today, similar yesterday. They happen irrespective of what he’s doing or where he’s sitting. He has been uncomfortable with the sore shoulder, but these episodes are a whole nother level.

Is it possible it’s his pacemaker? Battery is near end of life, he’s going in every 3 weeks to check it.

Any other ideas?