Exhaustion need only be accounted for in limited circumstances:
A character can perform a number consecutive (and/or simultaneous) actions equal to their Grace Period without penalty.
After the Grace Period expires, the character suffers a –1/ action cumulative on all further actions until he gets some effective rest. Then penalty stands for a number of actions equal to the Grace Period, after which it doubles. This doubling at every consecutive Grace Period continues until the character either rests or collapses.
So if a character has a Grace Period of 10, and commits one act a round, he would be –1 at round 11, -10 at round 20, and then –22 at round 21, and –30 at round 30, and –34 at round 31, and so on.
An action must require a roll to count towards exhaustion.
Very few action sequences actually last deep into exhaustion.
A character can buy an extra Grace Period, or turn back the clock one grace period, by taking one dice of damage. This can be done at any time. This damage cannot be assigned to a stat.
A character can also buy an extra grace period with a Fate.
Exhaustion penalties apply to all actions and stack, regardless of whether they are physical, mental or emotional. When the various Grace Periods have different values (due to different stats) the lowest current value applies. Sorry.
Exhaustion from Powers
In general, using an Extraordinary Power or SFX counts as two actions towards exhaustion; using a Supernatural Power counts as three actions towards exhaustion and using a Fantastic Power counts as four actions towards exhaustion.
If the power of SFX has a specific exhaustion cost, that supersedes the rules above.
Further, when using a power or SFX, each extra dice used in the SFX counts as an action. So if Cosmic Kid uses her Power Blast at +4 dice damage, that counts as 5 actions (one for the blast and then 1/dice) towards her exhaustion.
This does not apply if the power was used with a Chip.
Rest
Characters recover from Exhaustion by rest. Each Turn (or action round) spent in continuous rest reduces the exhaustion penalty by one. Rest, in this case, means taking no declared action - just sitting or lying there, you know, resting.
Being knocked out does not count as rest.