Dodgy hip

Did 20 Sunday. At about 14 miles, high up on the back of my left hip (psoas area I think) I felt as though it was spasming and then my leg was sort of collapsing under me? I had to slow right down for 20 or 30 yards before gently getting going again. It would be ok for a while but then it repeated intermittently over the rest of the run.

I was very protective of it for the rest of the run which was a bit restrictive to say the least and I lost nearly all drive through the hip going uphill.

I have began upping my mileage gradually since September last year to the point where I've been averaging 45-50 miles per week over the last 4 months.

Any ideas a) about what it is and b) what I do about it??