In Wikipedia, about the Kübler-Ross model, it’s said of the “5 stages of grief (denial, anger, bargaining, depression, acceptance)” this (the emphasis is mine):
Kübler-Ross claimed these steps do not necessarily come in the order noted above, nor are all steps experienced by all patients, though she stated a person will always experience at least two. Often, people will experience several stages in a “roller coaster” effect—switching between two or more stages, returning to one or more several times before working through it.
Significantly, people experiencing (or caretakers observing) the stages should not force the process. The grief process is highly personal and should not be rushed, nor lengthened, on the basis of an individual’s imposed time frame or opinion. One should merely be aware that the stages will be worked through and the ultimate stage of “Acceptance” will be reached.
I can verify the observation of bouncing back and forth, particularly with the death of my Mother recently. Prior deaths and traumas, my cousin by suicide in the 1990s; the implosion and dissolution of my first marriage; the death of my Grandfather last year, were in retrospect much “cleaner” and I think followed the classic sequence closely.
Currently I’m experiencing all five them, often the space of the same day or few hours. The lack of a coherent “plan” for how to view my day or week is very hard, but I’m managing to get some things done, thankfully.
So I push forward and onward.