Children's movie from the 90's?

I can't remember a movie from when I was a kid. I know it was kind of around the time of FernGully? It was sometime in the 90's for sure! It was animated, and it was set in a forest? There was a truck that tips over and spill something toxic and all the...

animals fall asleep, except for a few and then they go on an adventure to wake every one up? I'm sorry, that's all I can remember and I've been trying to find it for hours now. If anyone could help me it would be deeply appreciated! Thanks!

I think its Once Upon A Forest, I loved it as a kid, I had the same problem looking for Fern Gully's title last year.
I don't know if all the aniamls go to sleep, but there is a toxic truck and a little girl animal gets sick, and her friends in her class go out to find the cure to save her life.
Its like a teacher is educating them about the forest, and the children are set out to collect 2 herbs I think to heal the ill girl animal. The end of the film if I can remember shows the forest thriving once again
Hope this has helped., let me know

yep, once upon a forest, which was made in 1993
I used to love that movie as a kid, and still do
I've still got the video of it too