OK! four years CH free, four years no cigs (Chantix) and now the shadows are back! Tips:
Oxygen, Oxygen and Oxygen. I've has episodic CH since the early 1980's. Had eye doctors tell me it was optical and my current dentist tell me it was dental and a Neurologist who actually knows what CH is prescribe prednisone taper(I declined) and intranasal lidocaine---which hurts almost as much as the CH...but not quite.
Caffeine seems to help. Vigorous exercise seems to help. I've done a ton of midnight planting and digging during an attack. And walked a million miles cursing.
BUT hyperventilation level Oxygen ALWAYS aborts for me. If it doesn't work for you---keep trying and pay attention to what Batch has to say. Wrong flow rate, wrong mask...my former vet tech's father suffered for TWO years thanks to IDIOTS giving him the wrong mask and regulator. DO NOT LET THIS HAPPEN! If you get the O2 script---great!!! Then spend less than $60 for a mask setup and regulator and take responsibility for your own heath.
Perhaps, an antihistamine might be in order if there is a chance it is tied to seasonal allergies.
Perhaps a decongestant might be helpful.
Alternating warm and cold compresses over the trigeminal nerve local when all else fails or isn't available.
There are several herbal/supplement regimens that have promise---try them. Just started D3 myself.
If Oxygen isn't working try again. Do not be a victim!
If you smoke---quit. Try Chantix unless you are suicidal. If you have bad dreams, under Chantix they will be 3D vivid and terrifying. If your dreams involve Umma Thurman in a "non-threatening" pose...you will love Chantix. Do six months not three.
The people on this forum know more than "most" if not all doctors.
DO NOT go to the emergency room. They will screw you up completely.
DO NOT TAKE traditional prescription pain killers (opiats, Oxy, Etc.). They will make it worse.
DO NOT let some quack cut into you. NEVER a good idea.
TAKE CHARGE! Order you own regulator---25 lpm is mandatory minimum. You can find them on amazon. Rather than WAIT for a prescription, BUY your O2 at a welding supply company, Tractor Supply, Northern Tool, Harbor Freight, etc. You "lease" the tank and then pay a nominal fee to swap it out as needed. BUY the BIGGEST tank you can physically manage (at least a 3)---and then a smaller backup (a 2) which you can take in the car with you. NEVER RUN OUT OF O2!
Keep some Taurine inclusive energy drinks around for emergencies.

DO NOT TELL the folks at the welding supply store WHY you want O2!!!! Tell them you breed exotic Koi and need O2 to help them "get in the mood".