yes, this has happened on occassion and it was a nutrional issue (for me). i had to start playing around with what "foods" worked well for me prior to a workout & what seems to work best is approx 15-20grams of protein 30mins before hitting the gym. i take in a EAS low carb shake & a piece of fruit (normally 1/2 banana or a slice of apple w/peanut butter).
the more i work out the more calories i need; the under 1000 calorie a day plan wasn't working both at the gym & scale. Once I upped things to approx 1200 a day - my body responded happily.

just a suggestion - look at what your eating...
take care~!