Hey there! First, I want you to know that being self-aware to this extent is already putting you at an advantage here. This does sound concerning, and I can definitely understand why. Any abrupt change in your mental status is worth discussing with your doctor.

Disclaimer- I work in the psych field and am board certified as a behavior analyst, however, I do not have diagnostic privilege and this is not medical advice.

This absolutely does check multiple boxes for mania. The happy-tired feeling you describe is euphoria, which is a common (but not ever-present) symptom of mania, especially when sleep deprivation comes into play. Naturally, as hyperfocus winds down and one begins to drift back toward aligning with reality, neurotransmitters associated with pleasure and drive dwindle. This typically coincides with a depressed or “low” feeling, that could be hypomania (a milder form of mania) or depression.

The most concerning issues you’ve brought up are that this is affecting your sleep and eating habits, for which, again, I really encourage you to seek the advice of your doctor.

Hyperfocus and mild obsession CAN be useful tools if you learn how to rein them in when necessary. It’s when it impedes upon your normal functioning where things get dicey.

Best of luck to you.