I have since gotten past this but thought I'd post and see what others had to say. Few weeks ago I bought some Humco VG at Walmart to cut some juices. I tried vaping it straight and liked it because of all the vapor, there 0 nic, and it was a nice break from the strong flavors I use. After about a week or little over I started to notice this little tightness in my chest when I lay down to go to sleep. First thought was wheezing, but I really couldn't hear a wheez. Its kind of hard to describe, but it was a feeling I had in the past when i smoked. Maybe a very mild shortness of breath. Got to where it was becoming a concern, so I stopped vaping it, few days later it stopped. So I feel vaping straight VG was the cause. But I keep wondering what/why it started and if anyone else experienced this.