motion sicknesss

car sick is the adjective. motion sickness is good as a noun.

CJ

Thanks, CJ. What if you were in a train or a plane or a bus? train sick, plane sick and bus sick?

I think ..with any moving thing (car/plane/train) it should be motion sickness, as the real culprit is 'motion' here not the vehicle.

suhanii, I don't quite understand what you are saying. As pointed out by CJ, motion sickness is only good as a noun. I need an adjective to complete my sentence -- I'll get ___(car sick, etc)

motion sick is not a combination I hear, but it may be used. I think it's more idiomatic to rephrase it so you can use the noun.
CJ

i got your point ..the thing is if you write "motion sick" it can give an impression of 'diarrhoea or loose motion"
don't know.

Thanks CJ and suhanii. Any suggstion on how to rephrase?

Is it natural to say "I'll have motion sickness"?

i am unable to make out ..why are u saying 'sea sick' to car driver?
how will "I fear motion sickness" work

I wasn't sure which adjective to use which was why I asked the question and CJ said it should be car sick. Please refer to CJ's answer.

New2grammarIs it natural to say "I'll have motion sickness"?

Yes. Even better I'll get motion sickness.
CJ