Definitely true. I found that after a few weeks, I was waking up, stumbling out of bed, sitting in my chair, and taking a look at what was going on. After a few months, I realized that I felt awful every day, because I'd gone from bed to work without any break in between, and it was getting close to 4 PM before I was showering and having breakfast.
Enforcing an actual schedule on yourself makes a significant difference, and it's the only reason I managed to keep myself sane as long as I did.
The funny thing is that people often think you're living the dream by working from home. After all, you can work in your underwear if you want to! Indeed, I thought I had it pretty good and couldn't understand why I was so unhappy all the time.
It's my opinion that people who can work from home for long periods of time and maintain a healthy mental and physical state are the exception and not the rule.