sleep heavily
From Longman Dictionary of Contemporary Englishsleep heavilysleep heavilySLEEPif you sleep heavily, you cannot be woken easily → heavilyExamples from the Corpussleep heavily• Exhausted by the horrors of that day, I slept heavily.• When finally she slept, she slept heavily, dreamlessly.• He was still sleeping heavily, in almost the same position they'd left him in.• They had all slept heavily, the sleep if not of the just, of the innocent and artless.