Separation Anxiety

My daughters have never had major issues being away from me. Sure, from time to time they cry or act weepy, but all in all, they've never had problems. On their first day of preschool they walked into the room and never gave me a second glance. Unfortunately, something has happened to change all of that.
It started a few weeks ago. My girls were downstairs and I went upstairs to print something. I was in our office/guest room/catch-all room when I heard someone screaming at the top of her lungs. I could tell it was Roo and she sounded terrified. I ran from the room and she was standing on the steps, screaming and choking on her tears. "What happened?" I asked. "I didn't know where you were," she managed to choke out. There was nothing wrong, she was just upset that she couldn't see me. The rest of the day I made sure to tell her if I needed to go to another part of the house.
Then about a week ago we went to a picnic. When it was time to leave, the girls discovered they had left their party favors in the shelter. After everyone was buckled in the car, I went back to the shelter to grab the goods. I told them where I was going and they could see me the entire time. I was gone less than two minutes. I returned to the car to find Roo screaming and crying. "You should have been in the car" she screamed at me. A few days ago we were getting ready to go to the zoo. After everyone was buckled in the car I told them I needed to run inside to use the bathroom. Hubby was standing almost right outside Roo's window, but she screamed the entire time I was gone. (And in case you're wondering, no I don't leave them in the car by themselves for long periods of time... nor do I leave them in the car in a store parking lot). All weekend she has thrown a fit if I leave the room. I've made it a point to say things such as "I'm going upstairs to put this load of laundry away, I'll be back in a few minutes." She has asked if she can sit on her bed while I put away laundry because she doesn't want to be downstairs "by herself." On Saturday she didn't want me to go the grocery store. I asked her to come with me, thinking some mother-daughter one-on-one time was in order. Nope. She didn't want to go and she didn't want me to go, either. Keep in mind that during most of these experiences, Hubby is around. When he asks her why she is crying, she'll say "I want Mommy... I don't want to be by myself." She could care less if he's around. She wants me and only me. The day of the grocery store meltdown, I ended up taking her sisters with me and she stayed home to bond with Hubby. They played games, they played with Legos, they ate chocolate. They had a blast. There were no tears shed over the fact that I was gone. But once I came home, the tears started again... it has gotten to the point that I can't go to the bathroom without her crying.
Interestingly enough, bed time is not a source of tears. A few nights last week the girls stayed up waaaaaaay past their bed time because we had company. Roo requested to leave her bedroom door open and I left the hallway light on for maybe 10 minutes. She was fine with that, although she said she was "scared of the dark." (Never an issue, but it doesn't seem to be a huge issue now, either).
Yesterday Hubby and I got some clues as to what's going on. Roo says that at some point in time someone (neither one of us) was watching a "scary show on TV with bats and skeletons." The person in question denies watching anything unsuitable for preschoolers... so I'm back to square one. I'm just hoping I can get to the bottom of this and get my happy little girl back.