funny
[adjective]
slightly but undefinably unwell

• I don’t know why but I feel a little funny. Not sure it it’s something I ate.

grotty
[adjective]
unwell

• I felt grotty so went home early.

iffy
[adjective]
full of uncertainty; doubtful

• I’ve got a bit of an iffy stomach. Would you excuse me a moment.

lousy
[adjective]
unwell

• I feel lousy this morning. I think I’ll go home.

off colour
[adjective]
slightly unwell

• I’m feeling a bit off colour.

out of sorts
[phrase]
sightly unwell

• I’m feeling a bit out of sorts since eating that fish.

ropy
[adjective]
sightly ill

• I was feeling a little ropy earlier but took a nap and now feel better.

rough
[adjective]
unwell

• I caught some bug over the weekend and felt really rough for a couple of days.

sick
[adjective]
affected by physical or mental illness

• I feel a bit sick, so best not eat anything too rich.

under par
[phrase]
worse than is usual or expected

• I’ve been feeling under par these last few days.

under the weather
[phrase]
slightly unwell or in low spirits

• I’ve been a bit under the weather these last few weeks.

unwell
[adjective]
ill

• I just feel really unwell this morning.

can’t keep one’s eyes open
[informal expression]
very tired

• She could hardly keep her eyes open so I don’t think she’s going out tonight.

dead tired
[dead as an adverb]
completely

• I’d love to come but I’m dead tired.

done in
[informal phrase]
extremely tired

• You look done in. Go home and get some sleep.

drained
[adjective]
deprive of strength or vitality

• You looked drained. What have you been doing?

drowsy
[adjective]
sleepy and lethargic; half asleep

• It was a long meeting in an airless room which soon made everyone drowsy.

exhausted
[adjective]
very tired

• Although our meeting was productive, I’m exhausted.

frazzled
[adjective] [informal]
exhausted

• I’ve had three meetings, a long, horrible business lunch and had to write a couple of reports. My brain is totally frazzled.

pooped
[adjective] [informal]
exhausted

• I was pooped and didn’t move from the sofa all evening.

shattered
[adjective] [informal, British]
exhausted

• I was shattered after that meeting.

wear someone out
[phrasal verb]
exhaust or tire someone

• Every time I meet him I feel worn out.