That happens to me.  When I start to stretch I try to keep it low and slow and it is usually OK but sometimes it still gets me and I have to jump out of bed.  Again, since I started having a 6-8" glass of tonic before I go to bed the whole problem has gone away.  If I stop taking tonic my cramps come back (including the morning stretch ones).  I get a glass of tonic and problem goes away for a few days.

I am no doctor but I suspect the causes of cramps can vary from person to person.  Tonic works for me with truly remarkable results but it might not for everyone.  Certainly easy and painless to give it a try.  It started working the first night.  In fact I have gotten a cramp and went and got a tonic and it goes away within minutes.