This takes place some time after the S$ finale but is not based on any S5 spoilers. It's just my take on what Snow might be feeling.
Disclaimer: I don't own any part of Once Upon a Time, more's the pity.
Spoiler Warning: S4 Ep 23 Operation Mongoose Part 2
Night Terrors
Snow awoke to a piercing scream and it only took her a moment to realise to whom it belonged. Emma. She sprang out of her chair to where her daughter sat upright in bed, tears streaking down her too pale face and breaths coming in heavy gulps. Snow went to her without a word and pulled the poor girl into her arms as she attempted to soothe her. Emma continued to tremble but held on tightly.
"Shh, baby." Snow cooed, kissing Emma's hair as she rocked them back and forth. "It's all right. Mama's here now."
The words caused Emma to tighten her grip, as if fearing she'd disappear should she let go for even a moment. It was terrifying for Snow to see her daughter in such a state. Emma had always been so strong, but since they'd separated her from the Dark One, she'd been experiencing the most horrific night terrors. It had gotten to the point where she and Charming began taking turns watching over her whenever she was exhausted enough to actually sleep, which wasn't as often as Snow would have liked. She was scared and losing hope of ever getting her daughter back but she didn't know what else she could do. And she was angry, so angry. At Rumpelstiltskin, at Merlin and the Sorcerer. But she was mostly angry at herself. She should have stopped Emma from tethering the darkness to herself, should have taken it herself, should have fought harder, should have-
Snow's thoughts were interrupted when she heard Emma whimper in her arms, reminding her what was important in this moment. She couldn't focus on the what ifs, she had to concentrate on her daughter. Emma was all that mattered now so she shifted a little, as if to physically rid herself of her recriminations, and Emma's arms tightened on her once more.
"Don't go." the girl said in a broken voice, a voice that made Snow want to weep.
"Never." Snow told her daughter in a firm voice, smiling when she felt Emma relax in her arms. She could feel her breaths evening out and knew she was finally falling asleep. Whether or not that was a good thing was yet to be seen. All Snow knew for certain was that she would be there when her daughter awoke. She would always be there from now on.
The End