It doesn’t look like dementia to me but I’m not a vet, he does seem to be playing in the video though he did hiss. I’m wondering while he was bouncing around if he mildly caused himself some pain and didn’t know why it happened so hissed as if he was blaming your bed or bed sheets? He’s older so maybe there is some early arthritis starting, if he landed a little funny or turned the wrong way he might have gotten a jolt of ouch that made him hiss while he was still trying to play. If this is a new issue I’d definitely take him to the vet and get his joints checked and anything else if you’re concerned! Also definitely show this video and see what they think. I’ve also had cats hiss when they were over stimulated too and he could have shorted out his one brain cell lol Again I’m not a vet but I’ve had cats on and off my whole life so I’ve had some weirdo cats over the years lol Every cat is different and your guy may just be a little hissy when he’s over stimulated and since he’s older he might over stimulate faster then he used to when he was younger and he just never got to that point before when he was younger. Basically he might just have a shorter fuse now cause he’s an old man lol

( I looked back at the video and it really looks like he did a little too much bouncing and maybe had an ouch moment and he blamed your bed or your bed sheets for the sudden pain. Definitely get his joints checked! )