Hi,
My 18-m old son was napping regularly at 1pm for 2-3 ours. Last weekend we let him sleep over for the first time at someone else's place (my sister). It went well. Monday and Tuesday, he took his nap and slept fine. But on Wednesday he suddenly stopped, started crying as soon as we put him down for his nap and since then hasn't taken a normal nap (pretty much none in the last 5 days, except when we took him in the car or prem but not in his cot). And he is now started to do the same at night (crying and throwing all of his stuff out of the bed until we come). We usually wait 15-30 min before coming in and giving him a cuddle and put him back. We also tried letting him cry out, which works once but only after 2 hours. We're quite desperate and don't really know what attitude to take.