Sickness and Weightloss

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This last week or so I've had the flu and I've dropped a kilo and a half or so, not doing anything different, I am assuming it is the energy used to fight the virus. Can I expect that to stay off? Assuming I don't eat enough to make it come back. Or is it water weight that will just creep on over the next week or so.

I know it's only a little bit of weight, but I am so close to goal that it is taking forever to come off.