He smiled; just having someone to listen made him feel more alert.

Then his heart beat harder and he felt more alert.

Her brain felt alert, racing along the way it always did when she talked with John.

For no particular reason he felt more alert and in control.

I certainly feel more alert than I've done for hours.

At the same time, you feel more alert and focused.

He felt more alert, it seemed to him, than he'd ever been before.

Also, pay attention to which times of day you feel most alert.

With better sleep, you can feel healthier and more alert.

You may not feel alert or be able to think clearly.