I drank the potion that put me in dreamstate (?) and am supposed to open the Miasma gas !? but I don't know what to do nothing works in that state ...you can't access your inventory.or use anything , this is a quest from Dawnstar

You can run through the area. Which is what you need to be doing. Make sure you have the quest active in your log, so you get the marker....

Yep, run towards your compass marker and pull the chain. That's all there is to it

Drank Vaerminas Torpor potion now I can't figure out how to turn on the Miasma Gas ... ?? Any help ??

Uh.... read the posts just above your latest one?