It could have been an LP crisis by your description. My Chancy had LP. During my self-imposed crash course on the topic, I learned that it is not uncommon for LS dogs to also develop LP (Chancy also had LS). If your Jack has had recent flare-ups of wobbliness caused by LS, it seems easily possible that he is now having LP crises. Especially if he was already a "raspy" breather as you described.
For Chancy, keeping her cool and calm was key for a good long time. Thankfully, she never had a major breathing crisis episode, just gradually got harder for her to breathe. When she got to the point where her breathing was just too difficult, she had unilateral laryngeal tieback surgery. In her case, my only regret was not having done that sooner.