、。
When I woke up, I was lying on the sofa.
Literal
Eye [subject-が] wake-up [when-と], I [topic-は] sofa [on-に] was-lying.
目が覚めると ('when I woke up') uses temporal と to mark an automatic discovery — the speaker comes to consciousness and finds the situation already in place. 横たわる ('to lie down / recline') is more deliberate and more literary than the everyday 寝る — you'd use it for someone stretched out, as on a sofa or in repose — and the choice colours the register toward written/narrative. Pairing the literary verb with ~ていた (past resulting state) gives the line a quiet, almost cinematic 'I came to and there I was' feel.