I got a loan from my 401k for my wife's surgery.after repaying on the loan for 4 months it went into default because I was laid off my job.now I'm hit with a extra 10% penalty besides the 20% tax I have to pay on it.I claimed all the medical expenes on my tax returns last year. I had to get an extension for this year so I could figure this problem out.my question is:do I need an expert cpa on 401k distributions that can revise my previous taxes to include the taxes and penalty sense I claimed the medical and my taxable income was much less last year?

You CANNOT carry back the 401K distribution, because the initial distribution was a LOAN, not a taxable distribution.

Correct, when you got laid off you had the chance to pay off the loan and then roll over the distribution. By not doing so, you incurred a taxable event in the year you defaulted and got a 1099 for that year.