How is doze off different from just doze?
I think they mean the same thing— sleeping lightly. What's the difference between them?
We were watching a movie. When I turned to look at him, I discovered that he had dozed off.
To doze off means to transition from a wakeful state into a light sleep.
I was watching a movie in headphones. Now and then I turned to look at him to make sure he was still dozing.
To doze means to sleep lightly, but lacks this emphasis on transition from wakefulness to sleepiness.
Let's explore "still dozed", with and without off:
(still dozed) The two ponies still dozed at the hitching-rail.
The ponies continued to doze. "Still" is used in the sense "even then".
(still dozed off) She read the omnipresent billboards to keep awake but still dozed off a couple of times.
The woman was transitioning from wakefulness to light sleep and back a couple of times. "Still" is used in the sense "despite something" (despite her desire to stay awake).
Furthermore, per Damkerng T's comment and in agreement with Khan's awnswer, "dozing off" is done involuntarily, while you can "doze" at your will.
There is a little difference between the words "doze" and "doze off".
First, "doze" can be used as a verb as well as a noun, whereas "doze off" is used as a verb only.
Second, as a verb "doze" means to sleep lightly for a short period such as I like to doze after lunch in the afternoon. On the other hand, when we use "doze off" it means to start or fall into a light sleep without intending to such as she dozed off during the lecture in class.
Don't get much into the subtlety it has. Broadly, both mean the same. It's just that the verb doze is often followed by off. It's a way of writing.
Dictionary.com has this entry.
(often followed by 'off') to fall into a light sleep
The example follows
He dozed off during the sermon.