What can I say instead of “I’m very tired, I guess I’m sick”?
- I don’t feel good.
- I don’t feel well.
- I feel bad.
- I’m not good.
- I’m not well.
“Good” is an adjective meaning positive or desirable, as in “this is a good book”, or morally upright, as in “Fred has never hurt anyone. He is a good man”. Less often, “good” can be a noun meaning “benefit” or “well-being”, as in, “We must all sacrifice for the good of the whole.” “Well” can be an adverb meaning in a positive or desirable way, as in, “Since he took a class on public speaking, Fred talks well”, or it can be an adjective meaning healthy, “After taking the medicine he felt well again”.
English speakers, including native speakers, often confuse the adjective good with the adverb well. People will say, “She sings good”, when what they mean is, “She sings well.” If the idea is to describe the quality of her singing, then “sing” is a verb and so should be modified by an adverb such as “well”, not by an adjective.
I don’t feel good.
Valid. “Good” is a predicate adjective describing “I”. You don’t feel that you are in a desirable condition. In context, this sentence could also mean that you do not believe you are morally upright. “You are a very good person, Bob.” “Well, I don’t feel good. I think I have many ethical failings.” But that’s a rare usage.
I don’t feel well.
Valid. “Well” is being used as an adjective describing “I”. You don’t feel healthy. Note this is a different and possibly confusing use of “well” then if you said, “I don’t run well.” In that case “well” is being used as an adverb modifying the verb “run”, and so the meaning is, “My performance as a runner is not up to standard.” (Conceivably, “I don’t feel well” could mean that you are not good at feeling, like if you have nerve damage to your fingers, but that is a very unlikely meaning.)
I feel bad.
Pretty much the opposite of “I feel good.” Usually people say this to mean that they are not feeling healthy or otherwise are not in good condition. It is also used to mean morally bad. People will sometimes say, “Oh, I feel bad tonight” meaning “I am prepared to engage in acts that some consider morally wrong but that I think will be fun.”
I’m not good.
The most obvious meaning would be “I am not morally upright.” As in, “Do you believe that you are a good person?” “No, I’m not good. I have done many evil things.” In context it could also mean not capable or adept. Like, “We need another member for our baseball team. How are you at baseball?” “Oh, you don’t want me. I’m not good.”
I’m not well.
I am not healthy. “Well” here is being used as an adjective describing state of health.