Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

The phrase 'to break a butterfly on a wheel' is very evocative, but I can't bring myself to use it: I find the 'wheel' too disturbing. So: what are some good alternatives? (For those who are unfamiliar with this expression, Brewer's Dictionary of Phrase and Fable defines it as 'to employ superabundant effort in the accomplishment of a small matter'. [link]).
Use a sledgehammer to crack a nut. to do something with more force than is necessary to achieve the result you want When he sent ten men to arrest one small boy, he clearly used a sledgehammer to crack a nut. Better yet: Use a sledgehammer to swat a fly! idioms.thefreedictionary.com

Is there a single word in English to describe someone who is too worried about their health and even thinks they are sick, thus, taking frequent clinical tests or taking too much predictive medication,etc.
The word is hypochondriac and they suffer from hypochondria. noun A person who is abnormally anxious about their health. [ODO] ODO also gives the explanation of using hypo- ('under') rather than hyper- ('over') which one might expect if someone is overly anxious about something: late Middle English: via late Latin from Greek hupokhondria, denoting the soft body area below the ribs, from hupo 'under' + khondros 'sternal cartilage'. Melancholy was originally thought to arise from the liver, gall bladder, spleen, etc..

The context: Customer pays for some service 100$. If he chooses an option X, we charge him 20$ more, so 120$ in total. As a programmer I want my variables to have meaningful names. How would you call this 20$ in this context? I consider two words: markup (but it is more related to the business than customer IMHO) and surcharge.

The words that immediately come to mind are 'surcharge' and 'fee'. Consider the following: Basic cable service provides 50 standard channels for a set price of $30 a month. As for the premium channels, you may order them for an additional surcharge of $20. ...or the following: Standard repair service rate for a computer is $40 an hour. There is, however, an overnight fee of $10 for every night the computer is kept in our possession, after the repair is completed. We notify you after we have completed the service, and for every day that passes, you incur this extra fee. I am just utilizing random numbers on the example sentences, but I hope they help clarify usage.