The answer is quail.
The same confusion gains self, loses energy, and thus does enfeeble
The same = equal
Confusion = jumble up that word
Gains self = add "i"
Loses energy = remove "e"
... jumbled up, this becomes quail
And thus does enfeeble = whole word clue, with quail (vb) having the meaning of something becoming feeble.
OED
1. intransitive. Of a material (esp. living) thing: to decline from a natural or flourishing condition; to waste away; to fade, wither.
2. Of an abstract thing
b. intransitive. Of courage, †hope, †faith, etc.: to fail, give way, become faint or feeble.
