Can I sleep with an emergency blanket?

In an emergency you should roll yourself into an emergency blanket to sleep in if that's all you have, but it won't provide much comfort as it's not insulated or padded, so it's definitely not a suitable alternative to a sleeping bag and sleeping in Upholstered. That said, due to the very low cost and small package size, it's still worth keeping a first aid kit with you in an emergency.