Not a teacher only a native.
'You are sick, so take more rest.' Doesn't sound right to me, it is the 'more' I think is wrong.
I would prefer to say, 'You are sick, so take a rest.' If the person was sick already, then 'You are sick, keep resting.' could be used. However if the person had just become ill then I would use, 'You are sick, so have a rest.' Or, 'You are sick, take a rest.'
Hope this helps.
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