Extreme tooth sensitivity 2 days after using whitening strip on chipped tooth. What can I do? Could it be serious?

Typically time is the best medicine for post whitening sensitivity.  A bland diet (not spicy, not too hot not too cold) for two days, some advil or ibuprofen and sensodyne toothpaste should do the trick.  A quick visit to your dentist to take a look at the tooth with previous trauma is advised as well.

This can be a problem if the solution got down inside of the tooth. Try a rubbing a desentizing toothpaste onto the tooth. If that doesn't help, see your dentist.

Yes, over the counter products for tooth whitening can produce substantial sensitivity as I have also tried several and several whitening toothpastes with similar sensitivity.I would suggest using only Sensodyne ProNamel toothpaste for a few weeks or tube making sure to not completely rinse off all toothpaste just prior to bed and that should settle things down a good bit.I would also highly suggest having a dentist check your chipped tooth as incremental changes to the nerve can happen to teeth which have experienced trauma in the past.  Hypersensitivity can be an initial sign of pulpitis as well as a slight tint darkening of the tooth (but not always).No permanent harm usually comes from tooth whitening sensitivity and should resolve over time.