Your situation is not uncommon.
The fact of the matter is, you are both in a contractual situation. You as contractor and the other party as the client. By ceasing to perform your obligations under your contract, you are in breach - regardless of the reasons.
Failing force majeure clauses and the like, you don't have any legal standing in this situation. The client can in fact enforce damages upon you. But considering it's upwork and the contractual sum is not large (I assume), they chose to take their damages in terms of leaving you a bad review.
Best option for you is to contact the client and be transparent about your situation. If they choose to understand and retract their bad review, case solved. If not, you are left with a 'black mark' against your reputation.
Signing up for a new account does release you from their bad feedback - so no bad reputation. But the downside of a 'clean slate' is that you don't have a good reputation either.
I'm assuming that you may not have a strong reputation with a lot of work under your belt. If so, yes, start a new account.
A word of warning though, I'm pretty sure upwork will have a condition in their freelancer agreement that states no individual and/or company is allowed to hold more than one account AND that no individual and/or company is allowed to open more than one account within a certain period.
Easy solution, use your a spouse or a friend.
Good luck!