At the end of HLGEM's answer it's mentioned that when your answer goes awry, to just stop and regroup. I completely agree with that, and want to add to it and answer this part of your question:
Are there any good techniques that can be used mid-interview if I feel
myself getting nervous to get my mind under control?
If you are able to catch yourself before you get too nervous, or before your answer becomes too incoherent or just doesn't adequately reflect the knowledge you have, just stop yourself. If it's mid-sentence, just stop. If it's after a sentence, or before you begin answering, just take a moment to collect yourself.
The reason is this: interviews are often as much about how you answer a question as they are about the answer to the question. This is one of the reasons lists of common interview questions often include brainteasers (or, rather, seemingly absurd questions) like "How many times do a clock's hands overlap in a day?" You'd be hard-pressed to find a position in which it mattered to know how many times a clock's hands overlap in a day, but it is useful to watch someone try to answer it: do they jump to an answer (any answer) right away without explanation, and seem resolute in the answer? Do they ask probing questions to clarify the situation before they give an answer? Do they think out loud and work through some possibilities, and present possible answers with pros and cons for each?
So, if I am interviewing someone, and they are giving an answer to a question and say "Wait a second, let me backtrack to be more clear" or "Well, let me collect my thoughts for a moment", what that says to me is that I'm interviewing someone who understands something about careful consideration, clarity, communication, and so on. While on your end you might be thinking "Whew! I have a second to calm down", the outcome is the same -- you go back to controlling your mind, and the pace of your answer, so that you can ensure you give the best answer you're capable of giving.