Be seen. If you have "very severe pain" in your foot, I would probably be seen first just to confirm the diagnosis and rule out other potential causes of severe foot pain.
Ice. it, wear orthotic devices, perform achilles tendon stretches, wear a night splint..
Keep heels elevated. Plantar fasciitis is caused by strain on the attachment to the heel bone(calcaneus). Going barefoot, even only @ night, or wearing any flat shoes, ie., flip flops, sandals, bedroom shoes, etc., can keep enough strain on the plantar fascia to make it hurt. Rest the plantar fascia by wearing a small heeled shoe with all weight bearing.
Start with basics. Before you start treating your foot for plantar fasciitis, you must determine first, that you indeed have fasciitis. To a competent physician and even informed patients, this is relatively easy. Typically you will experience pain on the bottom of your heel when you get out of bed after sleeping. If this is not the case, the chances are that you do not have fasciitis. Remove doubt, see your doctor.