The disease, which attacks the nervous system, has forced the 51-year-old German psychologist to give up his career and most hobbies, including running and photography.

He spends his days in an electric wheelchair and rarely ventures out of his Berlin apartment.

"It's so difficult for me to open the door," he laments.

A caregiver comes to his home four times a day to help him with meals, cleaning and the growing number of other tasks he can no longer do himself.

But there is one thing that Daniel refuses to relinquish to his illness: the choice of how and when he will die.

"I've seen a lot of people with MS and who are not able to get out the bed, and this is no life, not for me," he says in a slow and soft voice that is indicative of the disease. He smiles when asked how he feels about his decision.

"There is only one word in me — freedom," he says.