Can our brains ever just stop working. like lock up. feel like mine does sometimes.

Not exactly: You can get transient problems related to blood flow and other issues, .

Not really: While it is common to feel like we stop progressing, our brains are generally always functioning. We may not have concrete thoughts that change our actions though.

Yes: Having said that however, this is predominately during periods of great stress. Some people referred to it as brain freeze or brain lock. This is however also more common among people with anxiety disorders and panic disorder. If you have any of those symptoms then please see a psychologist or psychiatrist to have them addressed. Antidepressants can cause this is a symptom. You can be halfway through a sentence and find yourself up against a brick wall when it comes to finding a noun or even an adjective that would previously been no problem for you to come up with.Antihistamines or another class of drugs that can cause this. If you are concerned about it is a medical condition, and you're not on any medications that would cause this, then you may want to have an eeg checked and see a neurologist just to make sure that you're not experiencing some sort of psychomotor seizure. Best wishes.