High intensity is very hard on the body when you're just getting started again - it is easy to overdo and get hurt. For myself, when coming back after a break in training, I find it better/safer to either reduce the intensity (so that it's more of an intense interval workout), or else increase the length of the breaks and decrease the length of the intervals, so that I'm going flat out for less time, starting fresher, if that makes sense. Sometimes that includes reducing the number of intervals so that the session is still intense but fits inside 20-30 minutes.
I'm looking forward to what Cathe nd others say here, as I'll confess the above is from trial and error for *my* own body, not science-based!