The strong impression given is that when Seven regenerates in her alcove, it also helps her to recover the strength in her limbs that normal humans would gain from lying down to sleep.
JANEWAY: Consider it done. The Doctor tells me you don't need to regenerate any more. I can arrange some quarters for you, unless you
enjoy curling up in the Cargo Bay.
SEVEN: A bed would be more comfortable. Since I arrived on Voyager, your guidance has been invaluable. Thank you, Captain. - Voy: Human Error
You may also wish to note that her blood is still filled with nanites that constantly repair her physical systems as well as a host of larger borg components (a "bi-radial socket" is mentioned). On at least one occasion (Voy: Hunters) we learn that she's gone over 56 hours without sleeping with only minimal ill-effects, so clearly she's not quite fully human yet.