Okay so my impression is that all HP (lets say 10) is a cumlative pool as well as duel status. Here is what I mean:
You start off. (10)
Cast a spell minus 2 hp. (8/10 hp)
Cast another spell to recover lost hp-3 hp. (5/10hp)
Heal for 5hp. (10/10) [5/10]
So while you are effectively at 10hp, only 5 hp are available for spell expenditure do to having spent 5 of your total 10 hp.
I think that is how it would work.
However this begs the question; If physical damage is sustained would it come from the 'bottom'(rest points) five of ten or the 'top'(healed points) five of ten?
I would argue the 'top' imagining it sort of as a cup of hp, drink whats on top first.
I would love to hears your thoughts, thanks!