If you take a nap and still have a reasonable amount of food in your system, your metabolic rate may well slow and your levels can change with this. There are differences in posture, sitting and laying down and how they affect levels, heart rate etc. If it slows, then that could raise your levels, but there are so many variables at play here and with a compromised metabolic system the effects seem to be more pronounced is what I have noticed.
Personally, this will happen to me, so I don't nap during the day. Plus it will keep me up late if I do nap, but since basically going keto I just don't have any need to nap like I did in the past.