Hi and welcome to the Chiari forum.
For now until u have more testing u may want to look at our list of things to avoid with Chiari/Syringomyelia...it is in the Health Pages as well as other helpful info -
http://www.medhelp.org/health_pages/list?cid=186
Not everyone with Chiari are surgical candidates and none of us really want this or the surgery either....since u have only noticed the symptoms for a short time could u have experienced a fall or illness such as the flu or been in a MVA which could have triggered ur symptoms?
So many of us have had symptoms our entire life, but were so accustomed to them we were not aware we had symptoms that connected to nething else....chiari symptoms do cycle making it hard to connect all the dots.
U should be able to do ur elliptical the problem may be ur shoulder area bcuz of the handle bars... u should be ok...a recumbent bike may be better for u....listen to ur body.....
U Dr will be RXing more tests..a CINE MRI and MRI's of the spine to rule out related conditions....
Know u r not alone <3