Why does ganger Doctor struggle to cope with his past regenerations?

Question

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: Hello.

DOCTOR: Cybermats.

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?

DOCTOR: Inevitably.

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?

Answer 1

Because the Doctor has a mind far more complex than that of a human being

The Doctor's intellect is far greater than that of an ordinary human (or perhaps even Time Lord), and he has lived many human lifetimes. As a result, not only does he have far more experiences than the average individual, he presumably remembers them much better. From Nightmare in Silver:

Doctor: (deeper voice) Incorporated. Yes. (pats himself down) Unfamiliar pulmonary set-up. Nervous system hyperconductive. Remarkable brain processing speed. Ooh! Amazing!

and

Cyber-Planner: Oh... this is brilliant! I'm so clever already, and now I'm a million times more clever. (spins across the room) And what a brain! Not a human brain, not even SLIGHTLY human.

The human brain is not equipped to contain Time Lord memories and knowledge. When Donna becomes the metacrisis Doctor-Donna in Journey's End:

DONNA: Brilliant, fantastic, molte bene! Great big universe packed into my brain! You know you could fix that chameleon circuit if you just tried hotbinding the fragment links and superceding the binary binary binary binary binary binary binary binary binary binary binary binary binary binary binary binary binary binary- [She gasps] I'm fine.

[She forces a grin and walks over to the console. THE DOCTOR watches her sadly.]

DONNA: Nah, never mind Felspoon, you know who I wanna meet? Charlie Chaplin! I bet he's great, Charlie Chaplin. Shall we do that? Shall we go and see Charlie, shall we? [She picks up the phone and speaks into it before putting it down.] Charlie Chaplin! Charlie Chester, Charlie Brown, no he's fiction, friction, fiction, fixen, mixen, rixten, brixten. [She takes a deep breath and leans against the console, breathing heavily and holding her head. THE DOCTOR walks over to her.]

Later:

THE DOCTOR: There's never been a human-Time Lord metacrisis before now.

[She turns to face him, teary-eyed.]

THE DOCTOR: And you know why.

DONNA: Because there can't be.

The Ganger Flesh was designed to incorporate a human mind. As such, it had trouble initially when trying to incorporate the Doctor's memories. However, it quickly proved more flexible than a true human brain, and was able to absorb the Doctor's memories and personality without endangering itself.