here is my guess at what has happened based on the info, as much as i can without being there anyways
it is likely primarily caused by 3 factors
1. insufficient ground insulation ... now i have used the neo air down to freezing alone just fine and lower with some heat loss, but i always fully inflate it ... the R value of an inflatable pad is usually correlated with its inflation (as you are a member you can see mr caffins excellent SOTM report on inflatable pads) ... thus yr partial inflation of the pad i suspect was part of the issue ...also just as many people require different amounts of insulation to stay "warm", so does the need for ground insulation vary
2. quilt loft ... the JRB sierra sniveler i believe is "rated" to 25-30F, this is not an en-rating, so im not sure how accurate it is ... there have been other threads on BPL with people noticing the loss of loft and with yr comment amount minimal down on top ... i suspect that the loft migrated from the top to the bottom over a few hours ... this likely got you feeling cold as im pretty sure the rating is for a fully lofted quilt
3. im not sure how much calories or fat is in the dinner, but you want to eat high fat foods like cheese, sausage, etc before sleeping ... and dont skimp on the calories either, yr body burns them while keeping warm ... drink enough as well as you need to keep hydrated, dehyration makes one cold
and aggravated by ...
4 getting up to take a piszz no doubt incurred some heat loss ... but i would have done the same thing in the temps you described ... holding yr bladder is worse IMO for sleeping warmth, yr expending the energy to hold it in
5 as to draft, what i mean is did you feel air coming in the sides of the quilt ... if you did the quilt is not wide enough, or youd be better using a bag IMO .... if you didnt, this doesnt apply
solutions ... i recommend these in order based on their effectiveness and minimal investment IMO
1. get a cheap foam pad (blue pad or a foam thermarest) and put it under/over the neo air ... this should effectively solved yr pad issues down to at least 15F or so ,,, minimal cost
2. drink and eat enough before sleeping ... i eat salami myself, and alot of it ... make sure it got fat content in there
3. you can get a piszz bottle if you want, mountaineers will take a pizz in the bottle inside their bag/tents and then use it as a hot water bottle .... however at the temps you described a hawt nalgene would be better IMO ... just fill it with near boiling water when cooking and stuff it in yr bag/quilt wrapped in something right away ... itll prewarm the bag for you and keep you warm for awhile ... be careful not to melt/burn anything though ...
4. if migrating down is an issue or you feel drafts coming in the sides (quilt not wide enough) ... consider a wider quilt or a properly en-rated sleeping bag ... the en-ratings give you a decent amount of confidence that the bag will be warm enough for the "average" person, whether you fit that mold is a question i cant answer ... also if the rest of the things here dont work youll simply need a warmer bag
as a side note and not as a dig to anyone ... i keep on mentioning the importance of technique repetitively ... gear itself will only get you so far
heres a few links on techniques and sleeping bag ratings
hope this helps ... be sure to report back what solutions work for you