Let me ease your fears a bit. Last year when I interviewed, everyone around me was coming out of rooms with wide ear-to-ear smiles and was saying how conversational and laid-back it was. I sighed in relief, thought of how good my other 2 interviews went, and entered my interview room. I was grilled over and over and over again by two vets who were completely unyielding and I was so taken aback that I stuttered through some of it and then broke down when I exited the room. A few weeks later, and I surprisingly got a phone call.
It's different for everyone, but the main point is that just because it seemed bad or really really hard, doesn't mean it actually went poorly. It could have just been the style of your interviewers. So don't lose hope!