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Please, try and remain calm. I know that you've got something scary happening to you, but I'm here for you and we'll see this through together.
I would never tell someone else anything about your medical condition that you wouldn't want them to know! We'll get you all scanned and checked out, and then decide what to tell your mother... I'm sure we can find a way that isn't lying but doesn't tell her everything. It's a hard line to balance for Doctors, but we're trained for this.
I'm not sure where 'there' is that you aren't growing hair on, but... we can see if there's a reason for that, too.