In series 6 episode The Almost People a ganger becomes the Doctor and starts going crazy
G-DOCTOR: Argh. What's happening? I wonder if we'll get back. Yes, one day. Argh. I've reversed the polarity of the neutron flow.
DOCTOR: The Flesh is struggling to cope with our past regenerations. Hold on.
DOCTOR 4 [OC]: Would you like a jelly baby?
G-DOCTOR: Why? Why? Why?
DOCTOR: Why what?
G-DOCTOR: Hello. I'm the Doctor. No, let it go, we've moved on.
DOCTOR: Hold on, hold on, you can stabilise.
G-DOCTOR: I've reversed the jelly baby of the neutron flow. Would you like a Doctor, Doctor, I'm, I'm the. I can't.
DOCTOR: No, listen, hold on. Hold on.
G-DOCTOR: No! Argh.
then suddenly its fine and he has a chat with himself
G-DOCTOR: Do we have time for this?
DOCTOR: We make time. I'd like more proof that you're me. Cybermats.
G-DOCTOR: Created by the Cybermen. They kill by feeding off brainwaves.
DOCTOR: Rory and Amy, they may not trust both of us.
G-DOCTOR: Are you thinking what I'm thinking?
G-DOCTOR: I'm glad we're on the same
DOCTOR: Wavelength. You see, great minds.
G-DOCTOR: Exactly. So, what's the plan?
DOCTOR: Save them all, humans and gangers.
G-DOCTOR: Tall order. Sounds wonderful.
DOCTOR: Is that what you were thinking? It's just so inspiring to hear me say it.
G-DOCTOR: I know.
G-DOCTOR: So, what now, Doctor?
DOCTOR: Well, time to get cracking, Doctor.
Which got me thinking: why does ganger Doctor struggle to cope with his past regenerations? Are all of his past 13 faces (William Hartnell, Patrick Troughton, Jon Pertwee, Tom Baker, Peter Davison, Colin Baker, Sylvester McCoy, Paul McGann, John Hurt, Christopher Eccleston, David Tennant, Matt Smith) too hard to handle? Why after going crazy the ganger Doctor is fine and has the Doctor's memories? How does the ganger Doctor have all of the Doctor's memories?