I had this too. Thought i was having an aneurysm. I noticed aspirin immediately helped so definitely a blood rush. Stretching my neck thoroughly before this type of workout helped a little but I found that exaggerating the inhale on the way down and exhale on the way up helped significantly. Also try holding a heavy barbell on your traps where there may be some trigger points. This also happened to me during high rep deadlifts. Proper breathing is an absolute must. I’m used to holding my breath with mostly low reps.