Happened every 4 years since 2004 but then most recently had them in 2014 which was 2 years from the last attacks. Mine lasts for 2 -3 weeks and happens around the change of seasons from winter to spring.
Worst attacks are during the night and just before dawn.
I take sumatriptan nasal spray and medical oxygen to reduce the length of attacks which range from 30mins upto 1hour. I also start taking prednisolone to limit the term of attacks down to 3 weeks.