What Causes Sudden Weakness In The Leg Along With Pain?

My husband and I were walking the other evening and all of a sudden he had no control over his left leg. he was stumbling and trying to get his balance back, but he said it was like his leg was not there. thought he was going to just fall to the ground. had no pain, although he did say that he felt a little weird. And then it was over and so far has not happened again. is it possible he was having a small TIA? or what could have caused this. Today he was very irritable and had no patience at all which is very unusual for him. Thanks for your help!