Can you use this ability while you are paralyzed? It takes an immediate action. Is is a "mental only" action?
If it is mental only then it should be allowed, but without being able to read the ability I can't be sure.
Absorb Blow (Su)
As an immediate action, whenever you take hit point damage from a single source (such as a dragon's breath, a spell, or a weapon), you can expend one use of mythic power to reduce the damage you take from that source by 5 per tier (to a minimum of 0 points of damage taken). If you have another ability or effect that reduces damage (such as protection from energy), reduce the damage with the absorb blow ability before applying any other damage-reducing effects. For every 10 points of damage that this ability prevents, for 1 minute you gain DR 1/epic and 5 points of resistance against acid, cold, electricity, fire, and sonic damage. The DR and resistances stack with any other DR and resistances that you have.
Sudden Block (Su)
As an immediate action, you can expend one use of mythic power to hinder a melee attack made against you or an adjacent ally. Add your tier to your AC or the ally's AC against this attack. The creature making the attack must make two attack rolls and take the lower result. Once the attack is resolved, you or your ally (your choice) can make one melee attack against the creature. The damage from this attack bypasses all damage reduction.
I've included another immediate action that is in the same vain. I don't know if "mental only" has ever been fully defined. But you have to take some kind of action. In this case an immediate. Hinder could be considered an action I suppose but that is not a keyword. I propose that neither can be used. But then again I think mythic is already easy mode and doesn't need even more ability to avoid death.
Mental only means is for things that don't require movement such as SLA's. Basically if you have to move it is not "mental only".