firstly, sudden onset of sundowning is unusual. secondly, "sundowning" that lasts throughout the night with violent and acting-out behavior is NOT sundowning.
classic dementia sundowning is usually a 2-hour thing or regular pattern and time, often with regular themes -- like being lonely, deserted, frightened and so on.
sundown is a time when many people experience emotional reactions -- babies are fractious, many people are sad, and elders with dementia have a highlighted emotional workout, often using the unhappy themes of their life.
it needs a planned approach. more sleep, perhaps an after-lunch nap, a snack of maybe fruit and juicwe about 2 hours before it usually begins. support, loving attitude and a diversionary program helps. someone who insists Mom (dead for 55 years) is coming to dinner can be helped by eating out and returning home after the sundowning thing has subsided. others need an arm around the shoulder, a box of tissues and you, listening and supporting. as in "Uh-huh", "Oh honey!", Really?", "I know you miss them," and so on.
Sundowning is when you'll hear real emotional truths about how this person feels at this time -- lonely, afraid, longing for the family they once had -- and all you have to do is be there. sometimes with an old family album so they are triggered to talk about those they miss so much.
Now, that jumping around all night thing is more usually a mental health issue -- maybe Bipolar, borderline personality stuff, perhaps schizophrenia long pretended away by family, PTSD in old soldiers and women abused as children. and it needs a more useful psychiatric intervention. i'm not keen on psych meds for elders, but by gosh, it can help bring peace and freedom from the terrors of psychiatric conditions to someone who has long struggled with them.
i cannot emphasise strongly enough that sundowning itself is NOT violent, aggressive, threatening and going on all night long. it is NOT. i really wish that this picture of so-called sundowning had not become popular myth, often in ther very families not willing or not able to discern real mental illness possibilities in their own parents or spouses.
i've worked with elders with dementia for 20-plus years. of the violently aggressive so-called sundowners i've personally dealt with (and folks, they are few and they are rare -- it's mainly myth that they are common and usual) one was a paranoid schizophrenic, one bipolar, two were PTSD and one more allergic to medication which made her violently act out while under its influence.
so if somethig new, violent and different starts to happen, you ask yourself, "What changed here?" If you can't figure out what ( new meds, UTI, whatever), a doctor is needed and preferably a good psychiatrist because they will have all the other tests done.
please, family members, dont put up with violent acting-out assuming it is sundowning and inevitable. it is neither. get help. you'll be glad you did.