Once, my dream was basically a mech combat simulator. I was driving some kind of hybrid between a Fafnir and a Supcom ACU, command automated tanks and artillery units to do my bidding, and of course wreak havoc within the supremely constructed command mech. I was armed with a plasma gun, a long range multiple launch missile launcher, and an AC-10 autocannon. I was doing well, with arty units covering the enemies I marked with my superior sensors in indirect fire, until some kind of crazy flying metal-plated slug came to me, started kicking my arty units' ass, and it had plasma deflectors.
Then I pumped it full of bullets and rockets, then I woke up.
Basically I was playing a video game in my sleep, with the difference that the brain was both the GPU and CPU, as well as the RAM and i/o devices. Maximalizes immersion really.