Breath-holding under heavy load swings your blood pressure, and the exhale at the top is when the head rush lands.
Straining with a held breath raises chest pressure and reduces blood return to the heart; releasing it drops that pressure fast, and standing tall under a bar at the same moment makes it worse. The NHS lists standing up too quickly, not eating or drinking enough, and heat as common fainting triggers, and heavy sessions stack all three. Continuous breathing, slower lockouts, real rest between sets, and food and fluids beforehand fix most cases. Recurrent dizziness, chest pain, palpitations, or an actual faint means see a GP.
What to do
Common questions
Why do I get dizzy during deadlifts?
It is usually a blood-pressure swing you are creating yourself. Holding your breath and straining through a heavy rep squeezes pressure inside your chest, briefly reducing blood return to the heart; when you finish the rep and exhale, pressure releases, blood rushes back, and your head can swim. Add standing fully upright fast at the top of the pull, a hot gym, dehydration, or an empty stomach, and you get the classic deadlift head rush. NHS guidance on fainting lists standing up too quickly, not eating or drinking enough, and being too hot as everyday causes, all of which stack up in a lifting session. The fixes: breathe continuously through the rep instead of a long breath-hold, exhaling through the hard part; do not whip your head up at lockout; rest between sets; eat and drink beforehand; and sit down the moment you feel grey. A brief head rush that passes in seconds is common. Dizziness that keeps happening, arrives with chest pain, palpitations, or blurred vision, or ends in an actual faint is a GP conversation, per NHS advice, not a programming question.