Crocea clam retracted

I have a 5" crocea clam which has been living on the sand of my 150
gallon reef tank for about a year under 250 Watt HQI. It has appeared
extremely happy during this time with full opening, and maintaining
its beautiful blue coloration. After getting back from a week trip
however in which there was a miscommunication with the tank sitter
about feeding, the clam is now retracted for the past 18 hrs. The
tank was not feed for 4 days (usually fed every other day. It still
opens a little and reacts to fish swimming close by, by closing more,
but it definitely is much more closed than usual. All other
inhabitants in the tank appear fine. All parameters in the tank (ph,
temp, ORP) were recorded by my aquacontroller in the normal range.
The only other unusual thing I noticed was that the clam was at about
a 40 degree angle from facing the top of the tank. This has happened
before, but I normally would be home to straighten it up within a day.
Is it possible that it has been starved due to light deprivation, or
deprived of a low level of nitrates since the tank was not fed? Will
it recover?