Shattered Kingdoms

Spells are already that way.

If you take a large amount of damage, are tripped, or engaged by many foes, your spell is disrupted.

Each foe fighting you directly increases the strain on your concentration.

Being bashed or tripped places you in the resting position which decreases your maximum ability to concentrate and risk losing your concentrated spell.

Any time you recieve a bright red "damage" message, such as "That really did hurt!", you incur a temporary decrease to max concentration and risk losing your concentrated spell.