It is a very common for anxiety sensations to be misinterpreted for a variety of organically caused 'symptoms'.
When anxiety is physically manifested as palpitations etc this is usually feared as indicating a heart problem.
When anxiety is physically manifested as an autonomic nervous system disturbance this is usually feared as indicating an organic neurological condition.
There are hundreds of neurological conditions
but for some strange reason there are 2 that always seem to be favoured by the health anxiety sufferer. ALS is a particular nasty disease that is often feared by the HA sufferer, this disease is seen as a living death sentence and the ill informed information is that this disease is defined by muscle twitching which is a common anxiety sensation. The reality is that ALS is defined by very noticeable clinical/objective weakness which progresses very quickly and is totally different to the fuzzy/subjective weakness that will often experience with anxiety.
It is widely recognised within the medical community that many anxiety sufferers who experience autonomic disturbances due to anxiety fall into the trap of interpreting these sensations as MS. MS works on a different 'fear level' to ALS whilst we fear ALS as it is terminal, we fear MS as it is hard to diagnose and very unpredictable...by nature the anxiety sufferer is likely to be the sort of personality who struggles to deal with issues such as uncertainty and unpredictability and therefore MS is in many ways seen as the worst possible illness, not because of the REALITY of the disease but because of the fact that it means out life will become unpredictable and that we will lose control.
What muddies the water with MS is that, as you highlight, the sensations that we experience when we suffer from anxiety are very similar to the 'symptoms' of MS....there is of course a good reason for this and that is that they both effect the same part of the body BUT, the 'symptoms' that are caused by MS are organic in origin whilst the sensations that are caused by anxiety are actually mental in origin but which are having a physical effect...this point is crucial and is, I believe why, we fall into a trap...we spend far far too much time convincing ourselves that our problem resides in the physical what in actual fact we need to escape this mindset and take a leap of faith and move into counteracting our thought and emotions.
My health anxiety started due to a personal health scare and also a friend dieing. It is widely acknowledged that a medical stressor either personal or family etc can lead to health anxiety developing in an individual. The fact that you have a cousin who has MS and that you are fearing your sensations as MS will, I believe, predispose you to a faulty interpretation of these weird and wonderful sensations you are currently experiencing.
Take some time to look around the forum and you will see two distinct things, a plethora of people with anxiety related disorders who are experiencing the same sensations that you are and also just as many people who are interpreting these sensations as MS. Of course, nobody on here can say you don't have MS with 100% certainty as anybody could have MS and not even be aware of it as they are not health focused individuals....some people will go to the GP with a foot tingle (guilty

) whilst other people will pay zero attention to things that freak us out and would only go to the GP when they notice something that makes it objectively obvious that something is wrong.
All I can suggest is that you just try and remove yourself from your situation for 5 minutes and look at the bigger picture, look at what these sensations are likely to be considering any stress etc you have been under and do not place as much emphasis on what you fear them to be as this is far far more unlikely....ask yourself how you feel about MS and if you feel your cousins situation is effecting how you feel about the disease etc etc. All things that may seem obvious but also things we overlook when we are scared and anxious.
I'm sure things will resolve themselves and that you will be fine.