i never understood either how elizabeth went from believing she was naomi collins to fearing being buried alive.both fears are on the same wavelength but i don't believe they ever explained this change.
It may not have actually been a change. Check out this post
... in Ep #514 Liz exhibited signs of being terrified at the thought of being buried alive
for a possible explanation.
once angelique loses her powers i'm not sure either why this particular curse continues to play out.
We don't really know in terms of the storyline why it continues to play out, which might be a bit frustrating - but in real life terms there was a good reason: Joan Bennett wanted/needed time off, and the whole Cass/Ang puts a spell (or spells if one considers the Naomi spell different from the obsession with death spell) on Liz was devised to accommodate that by first sending Liz to Windcliff and then putting her into a supernaturally induced coma. As we've mentioned before, it's often the case that real life events intervened on the plotting of DS and caused certain scenarios to take place or not to take place. But then, DS isn't unique in that respect because it's pretty much the case with all soaps.