This question is refering to part III of the book, after his conversation with Porfiry.
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"When Raskolnikov got home, his hair was soaked with sweat and he was breathing heavily. He went rapidly up the stairs, walked into his unlocked room and at once fastened the latch. Then in senseless terror he rushed to the corner, to that hole under the paper where he had put the things; put his hand in, and for some minutes felt carefully in the hole, in every crack and fold of the paper. Finding nothing, he got up and drew a deep breath. As he was reaching the steps of Bakaleyev’s, he suddenly fancied that something, a chain, a stud or even a bit of paper in which they had been wrapped with the old woman’s handwriting on it, might somehow have slipped out and been lost in some crack, and then might suddenly turn up as unexpected, conclusive evidence against him." (Part 3, Chapter 4, Line 29)
The quotes above takes place in the story directly after Raskolnokov has a conversation with Razumihin in which he says, "It is in just such stupid things clever people are most easily caught. The more cunning a man is, the less he suspects that he will be caught in a simple thing. The more cunning a man is, the simpler the trap he must be caught in. Porfiry is not such a fool as you think.…”
The fact is, he alarms himself. He's so busy being cunning, that he see he may have made a mistake, and that the mistake, no matter how small may just get him caught. I believe his terror is deemed "senseless" because he didn't leave anything behind, and he's losing it..... over thinking and over reacting.
Crime and Punishment