Sentinel had nebulously left the clinic a nebulous time ago, probably far too early. His basic logic was his insides weren't about to fall out again and he wasn't in immediate danger of dropping dead, not to mention being utterly sick of everyone involved (looking at you, Megatron).

Things are starting to rattle around again, however, and he's decided he needs a check up. He's also decided Red Alert is the medic he trusts the most here, lucky for her. He'll be nice and knock instead of just striding in and demanding help. Amazing.