That sound strange to me...not this fatigue, that's common. But he can't sit or walk? Could there be a spinal compression? Your dad's fairly young with limited Mets. Is he on a lot of pain meds. I'm sure others will chime in, but I'd be wanting to know why he isn't showing improvement too.
Husband age 56
Dx: PC with widespread Mets to bones and nodes 11/2010
PSA @ dx 1983 Gleason 4+5 stage IV
Xtandi 9/13 xofigo 1/14
Ongoing since dx: denosomab and Luprolide
Begin RT to sacrum X 10 1/15 PSA 1/15 100 +
Pilot study DRibbles vaccine begins 3/15
CT shows liver lesions not present in Dec.
Current psa 900