Disclaimer: Just playing in the JKR's sandbox.
Waking with Severus is not the delicate, dreamlike state that others would believe it to be.
He twists and he turns, groans and mumbles, and the coarse and - thank Merlin - sparse hairs that provide the nest for his erection scratch against the soft skin of Hermione's thighs. While his hands wander, cup and search, his chin rubs on her shoulder blades like a cat in the midst of sunning itself rather than a husband seeking out morning connections.
Others assume and even dare to ask her whether he snaps to attention immediately, a relic of the old days.
But Severus Snape awakens slowly now, ten years post what Hermione has nicknamed VWII. His breath tickles her back, and he smacks his lips together as if miming a kiss. His body cups hers from behind and he sighs, pushing his cock into the crease of her backside, sliding in and out.
When she takes him by surprise and shoves her arse against him, he growls into her ear; really, she is just looking for retribution for her husband daring to wake before even the baby does.
He enters her slowly, and calls her out to play.