What does it mean to dream about hydra?
A hydra in a dream often pictures a problem that multiplies, a trouble that grows two new heads for every one you cut, and the fatigue of fighting it.
Four ways to read it
Each reading below comes from a named tradition and a cited source, so you can see where it came from and decide what fits your dream.
Freud
Freud would read the many-headed serpent as a drive that cannot be quelled by attacking its surface, since each cut breeds more. The endless heads may stand for a wish that returns however you suppress it. Ask what trouble keeps coming back no matter what you do.
After Freud, The Interpretation of Dreams (Brill trans., 1913), public domain.Jung
Jung might see the hydra as a complex that resists being hacked at piecemeal and must be met at the root. Fighting symptoms only multiplies them. The dream may suggest looking beneath the heads to the source that feeds them.
Jungian concept (our summary).Modern
Threat-simulation theory suggests the dreaming brain stages an overwhelming, self-renewing threat, matching a waking problem that seems to grow as you tackle it. It can follow stress that feels endless. Notice whether you kept swinging or found another way.
Threat-simulation theory (our summary).Mythological
In Greek myth the hydra grows two heads for each one severed until Heracles burns the stumps to stop them. The labour turns on changing tactics, not just striking harder. The image tends to ask whether your effort is feeding the very thing you fight.
Rosmerta Publishing editorial synthesis (after Bulfinch; Brewer).