I would schedule an appointment with your vet or a specialist recommended by your vet to have the diagnostic test done to see if LP is what you're dealing with. The symptoms you describe are consistent with what my boy, Keno, demonstrated. Also with summer approaching, dogs with LP are heat intolerant and cannot use their breathing to cool themselves and can overheat and quickly go into respiratory distress. If it is LP and he's healthy otherwise, he may be a candidate for surgery. LP is serious and attacks can be fatal.
You can also search for Laryngeal Paralysis and/or LP under Health and Medical to review other threads about it.
Let us know what you find out. Sending good thoughts to you and your boy.