During the Covid-19 pandemic
The NHS has advice about mental health if you're isolated from others. They also suggest some good apps.
You might also find it useful to look at some more general information on various areas of mental health:
I recommend having appropriate therapist support in place before reading books which may open up deeper issues in ways you had not expected.
Extreme anxiety whether in young adulthood can be deeply disabling. Eleanor Morgan's Anxiety for Beginners (Bluebird, 2017) is an account of her struggle to find explanations and treatment for panic attacks, and her journey towards living with and managing her anxiety as a meaningful part of her life.
Bereavement and loss
A bereavement can result in a confusing mixture of feelings, including deep sadness, anger and fear, and it can be helpful to hear from other people with similar experiences. This kind of support can be found in a group setting, but also in books like Grief Works by Julia Samuel (Penguin Life, 2018). The books includes practical advice about how to cope in different situations. If you've lost a parent in young adulthood, and particularly if it leaves you feel different from everyone else your age, Rebecca Abrams has written, When Parents Die (Letts, 1992).
Death is a subject we tend not to talk about. Staring at the Sun: Being at Peace with your own Mortality (Piatkus, 2011) is a thought-provoking read by Irvin Yalom, an eminent and very readable existential therapist.
Shame is universal, but can lead to unhealthy feelings of contempt or self-loathing, and the belief that others feel the same about you. Brené Brown's famous Ted Talk The Power of Vulnerability is a great place to start to thinking about this area.
In Sue Johnson's Hold Me Tight (Piatkus, 2008) she prioritises the importance of a sense of safety in relationships, describing how it develops and preserves the bond between you and important others. Landscapes of the Heart by the relationship therapist Juliet Grayson (Jessica Kingsley, 2016) explains her thinking as a couples therapist, with a particular focus on encouraging emotional honesty between members of a couple.
Family rifts and estrangement in adulthood
A total relationship cut off between close relatives is surprisingly common but not often talked about. One of the most readable books about estrangement in adulthood is Healing from Family Rifts by Mark Sichel (McGraw-Hill Education, 2004). The book also offers advice on how to reconcile, and if this is not possible, how to come to terms with the shock and ongoing sadness of being estranged. A more recent book, also highly recommended and perhaps more optimistic, is Karl Pillemer's Fault Lines: Fractured Families and How to Mend Them (Yellow Kite, 2020).