What is Victor describing when he says that “Surely nothing but the unbounded and unremitting attention of my friend could have restored me to life”?
On the most literal level, Victor is simply ill and he needs help. He's referring to his current situation.
On the emotional level, Victor is referring to how unbalanced he is, on the emotional and spiritual level, after creating life in the lab.
On the symbolic level, Victor is referring to himself—he needs someone to restore him to life as he restored the monster to life.
He feels very stunned and feel "out of the world" as he had created a monster with life with his bare hands which people deemed impossible. Somebody had to bring him out of the fantasy into the grim reality that he had created a creature, a real monster. His mind feels very unbalanced as he ponders over his motives and feelings of creating this monster and to what cost, so with the attention from the monster, he will accept this reality check and be back to the present, as he had known that he had created a creature that humans no longer thought off and that creature serve as a tool for memory and recognition of what he did and achieved.