Subject: Why is lightning in my pillowcase? And should I worry about sparks?

Last night, I thought I was seeing things.  The bedroom was totally dark.  I went to fluff up my pillow 
and it flashed brightly.  I thought an mini LED keychain light had fallen in it and I had pressed it-that's 
how bright it was! I determined that it was the pillowcase and not the pillow, and sitting in the dark I 
repeated this weird phenomenon shaking the pillowcase repeatedly, which woke my wife.  In response 
to her question as to why I was sitting in the dark, I said there was lightning in my pillowcase.  She 
thought I had lost it, until she saw it with her own eyes-repeatedly.  Just shaking it in the air caused 
numerous sparks of bright light!  well, I changed pillowcases, before putting my head on it!  It's cotton, 
15 or more years old, very thin and soft but not all cotton, but rather a blend.  I set it aside and plan to 
recreate the lightshow again tonight. How rareis this phenomenon? And, should I worry re: the 
environmental atmosphere in my home that has caused this?  Thanks!l 

Re: Why is lightning in my pillowcase? And should I worry about sparks?