Word Choice – How to Use ‘I’ and ‘Me’ in an Answer

While those might mean the same for the laymen, from a medical point of view, there is a difference between illness and sickness.

Medical sociology has long made the distinction between illness and sickness. Illness is the objective diagnosis that an external impartial observer is able to make based on the constellation of symptoms which the patient presents. Sickness is the social role that the patient adopts as the patient and other concerned stakeholders, in relationship with the patient, interpret the meaning of the illness.

From what I get of it, someone might see themselves as sick (with the social/role aspect of it) but not actually be ill (in a medical sense). Also, this paper might provide some useful reading.

In my opinion, none of the above sentences are correct.

Like can be a preposition, and is used before nouns and pronouns to talk about similarity. For example:

He ran like the wind.

or

A person like you knows that..."

As, on the contrary, is a conjunction. It is used before a clause and before an expression beginning with a preposition. For example:

Nobody knows her as I do.

or

In 1939, as in 1914, everybody seemed to want war.

It is true, however, that in informal English, like is frequently used as a conjunction instead of as, so the first sentence "Do like we do." could be heard.

The third sentence is wrong because you are making a comparison and in this case as is the only one you can use. If on the contrary the concept which you want to convey is that the girl is tall and that your sister is tall too, then like is perfectly fine, but you need a comma to separate it from the first part of the sentence (that is, "She's tall, like your sister.").

Finally, you normally also use as when talking about the function or the role of something. For example:

He works as a waiter.

or

Don't use that knife as a screwdriver.

Disclaimer: The grammar explanations and most of the examples are taken from Swan's "Practical English Usage".