Depression and other complications of mortality can wreck havoc on one's ability to repent (change) and have joy - and they can lead to crushing guilt that can be seen at the extremes of self-criticism and self-hatred.
Praying harder, studying more, "obeying" more intently, etc. are not the proper initial or all-encompassing answer for people struggling with these types of issues. Finding good medication and/or coping techniques must be the foundation, since such problems won't disappear or become manageable until the imbalances that are causing the issue(s) are controlled to whatever degree possible.
The same can be said of almost anyone and any issue (that proper coping techniques are vital), but actual physiological issues must be approached differently and openly and without guilt or shame being added by others when traditional answers just don't work.