Idugupadiamond
ahhhh, that is where the teacher is not being clear.
It should not be called 'relaxing' as that is a Western Concept
it should be called pranayama and meditation
at which point its great fun
if I get too much of a "lie back and relax" I start doing breath control exercises and the time flies by : and they are an ab workout ....
basic one is
breathe in for three, hold for three, out for three, hold for four
repeat three times
then all to a count of four and repetition of four
then five
then six
at seven you do in seven, hold 4, out seven, hold 4
ditto at 8
at 9 you do in nine, hold 5, out 9, hold five
and then 10 - 5 - 10 - 5
and then all the way back down again to three
it should take about 15-20 minutes and will leave your brain utterly clear (you cannot do all that counting and make a shopping list at the same time) and your abs will be screaming 
the short version goes up the breath length without the repetitions