You can try Effects > gverb, echo or phaser -- in Audacity 1.3. Not 1.2.
Half of the effect is the actor, though. Nothing kills the effect faster than the actor saying flat lines in a dream sequence. Sometimes the actor messing up is played for comedic effect. Effects and filters over a normal, conversational voice. If you're in a serious voice-from-the-dead or dream scene, you can't do that. Experiment.
Audacity 1.2 is very old and no longer supported,
patched, corrected, or updated. Audacity 1.2 can
be unstable on newer computers.
Download and install the latest Audacity 1.3 from here...
http://audacityteam.org/download/
You can install both audacity 1.2 and Audacity 1.3 on
the same computer, but only use one at a time.
Audacity 1.2 will not open projects made on Audacity 1.3.
If you use MP3 or some of the more modern audio
compression formats, get Lame and FFMpeg software
from the same web site. Do not use older software
or software from other web sites, even though they
may have the same names.
Koz