Stephen has not slept in bed for weeks

The boys got sleeping bags for Christmas. After the initial spate of floor sleeping, Arthur now will only very occasionally trot his out for a change of pace. But for quite some time now (weeks? months?) Stephen has not once slept in his bed. I think he's scared to, for some reason. He doesn't even bother with the sleeping bag any more; he just puts a couple pillows on the floor and sleeps on those. Last night, we did the tent thing -- putting chairs around them (Arthur tried too, since this was new) and draping blankets on top.