1- When we experience fear in a dream, the physical manifestation in the dream state itself such as rapid heartbeat and sweating can actually be absent. It is only on awakening that we realise that we have reacted physically.
2- When we realise we are perspiring in a dream, we arc acutely aware of our reactions to external stimuli. We are alerted to the need to handle our own emotions and fears.
3- Spiritual effort can manifest as a physiological reaction such as perspiring, which indicates the amount of energy being expended.... Ten Thousand Dream Dictionary
Mostly fear. As we get near to experiencing areas of our memory or inner feelings which disturb us, rapid heartbeat and perspiration are some of the first signs. Occasionally pleasurable exenion. Idioms: in a cold sweat; no sweat; sweat blood; sweat of one’s brow; old sweat, sweat it out. ... A Guide to Dreams and Sleep Experiences