The actor, who is currently expecting her first child with her partner Matte Babel, also touched upon the difficulty of being pregnant in the public eye.
Earlier this year, the Pretty Little Liars star announced that she was expecting, sharing a photograph from a fashion shoot on Instagram and a two-minute video on YouTube titled: "Guess Who's Preggers."
The previous year, the actor had experienced a miscarriage 14 weeks into her first pregnancy.
In a new video shared on her YouTube channel, Mitchell explained that being pregnant can have a negative impact on one's personal sense of identity, especially when an expectant mother is keeping the news of her pregnancy a secret.
"This is the s****y side of being pregnant when no one knows, because you can't go out to see anyone, you don't want to see anyone. I don't feel like myself," the 32-year-old said in an emotional clip filmed prior to her pregnancy reveal.
"It really sort of messed me up a little bit," Mitchell stated, with regards to not being as sociable as she had been previously.
In the video, the actor also detailed the shock she felt when she experienced a miscarriage, as she was "completely blindsided by it".
Having been just over three months into her pregnancy, Mitchell said hadn't been aware of the percentage of pregnancies which end in miscarriage.
According to the Miscarriage Association, around one in four pregnancies end in miscarriage.
"I still have those photos on my phone [of ultrasound scans] and I still have all the doctor visits and it's weird because I haven't looked at them, obviously. But it's not like I forgot about that happening," the You star stated.
"So of course I'm like super happy, but I still feel for that one that I lost."
In the video, Mitchell led a tour around a bedroom which she described as the "baby's room", which has not yet been decorated.
The actor explained that she wants to wait "as late as possible" to prepare the room for her first child due to her miscarriage experience.
Mitchell stated that experiencing a miscarriage is "really tough because you feel broken as a woman".
You can call the Miscarriage Association helpline on 01924 200799. The helpline is open Monday to Friday from 9am until 4pm.