Palli konda Perumal

Why Perumal alone has this sleeping posture? - from KrishnaPremi
This is to signify that Bagawan is sleeping during pralaya kaalam.
When bagawan decides, its time to cause pralayam, with fire everywhere and then he first fills earth with water, water absorbs in air, air escapes in space and space gets absorbed into perumal itseems. (Very similar to black-hole concept)
After perumal has initiated this pralayam, and absorbs everything onto him, he goes to yoganithrai itseems.
In srirangam alone, perumal lies in snake with no body surrounding him, which means Perumal has succesfully caused pralayam and everyone is absorbed in him itseems.
In other palli konda perumal kovils, we have Bramha coming from Perumal's naval, sridevi boodevi and other devargal.
This means, Perumal has woke up from his yoganithirai and started doing srishti at the end of the pralaya kalam itseems..