Re: What exactly is Regeneration like to the Doctor?
My take on the 'screams' and violent nature of the transformation is that it would be painful. As Ten said to Rose, every single cell in his body changed. That would be intensely painful. As for 'what happens' to Time Lords, I think that Ten was right on the money when he told Wilf that 'another man' goes swanning off after the regen is complete. The individual is gone, but the memories remain.
So yeah, I think that regeneration is death for all intents and purposes. The person who was The Doctor dies and someone else who shares his memories is born.
Some say that he haunts the halls of the Top Gear production office and that, if you listen closely, you can hear his wails around Gambon.
All we know is that he's not The Stig, he's The Stig's drowned predecessor.