Can Asclera used during vein sclerotherapy cause a severe reactions?

It seems like you had a combination of side effects - delayed allergic and also perhaps a PFO related embolizatio of foam admixtureinto your cerebrovascular circulation. Even if you read this post 6 months after you posted it, you should get a 2-D transthoracic echocardiogram with a bubble test to look specifically for patent foramen ovale and if this test is normal, get a transesophageal echocardiogram to look for the same (TEE). I would also consult a neurologist if symptoms persist or recur. Talk to your primary care physician and a Board Certified Vein Specialist from the American Board of Venous and Lymphatic Medicine. 

Asclera (polidocanol) can cause side effects especially if it was used as a foam.  The tiny bubbles in the foam can pass into the venous circulation resulting in headaches and sometimes visual changes such as spots in front of the eyes and blurry vision.  These symptoms are usually very transient, occur within one hour of the procedure and resolve within about one hour.  The headache, however, could last longer but I have not heard of the headache lasting for this long.  Fortunately, the side effects from Asclera are infrequent.  I cannot explain fever, chills or shaking as being due to Asclera. Side effects are worse in people with asthma and history of migraines.  You definitely need to follow up with your treating physician.