When you realise that you are over-stressed, actually point it out to yourself.
Stop for a moment, and notice what you are doing and how you are feeling. As soon as I realise I’m snapping at my husband or children, I stop whatever I am doing (because I’m usually doing something like the washing-up at the time,) and I stop whatever’s in my head and I take a deep breath, turn to the person and apologise. “I’m sorry I wasn’t fully concentrating on you. Please can you tell me again?”
If I believe that what I am doing is the priority, I pause, take a deep breath (getting more oxygen is key to de-stressing) and say something such as, “I’m sorry I wasn’t fully concentrating on you. Once I’ve finished this I will let you know that I am ready for you.” (Please remember that the timing needs to work for them too!)