Laughing in a dream usually reflects relief -- tension breaking after a stretch of holding something in, or joy that's been waiting for a moment to surface. It can also point to a lightness returning to a situation that's felt heavy, a sign that some of the pressure has genuinely eased.
The aspects of the sextile or trine have the same quality: but the sextile is less forcible than the trine, either in good or evil. - William Lilly (1602.-1681.)