PROBLEM:
If you look, you can't see me.
If you see me, you cannot see anything else.
I can make you walk if you can't.
Sometimes I speak the truth.
And sometimes I lie.

What am I?.
.
.
.
HINT 1:
Question: Is "I" something tangible, that can be felt or touched?

Answer: No.
.
.
.
HINT 2:
Question: Is it something that happens at specific times?

Answer: Yes.
.
.
.
.
SOLUTION:
A dream