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1.
When someone is getting less concentrated, confused, or committing mistakes all the time then he is losing his marbels. It is related to the mental status of this person. It does not mean he is metally ill though.
I can not pass this exam. It seems I am losing my marbels

Stop thinking of her, you are losing your marbels

If I stayed unemployed any longer, I will lose my marbels
by bambastik January 14, 2010