Hi, klo
Before we get to the depression part .... the foggy thinking may have to do with the cisplatin; as I understand it there are ways of compensating for it. Does your hospital/cancer center offer any seminars on this?
Is your dear Alex seeing a neurologist/pain specialist for the pain management. One of my riding buddies specializes in this, and her arsenal includes conventional drugs, acupunture, and even lavendar pillows!
Re: the fatigue - has he had the thyroid test yet?
Ok, now the depression. My husband (the survivor) managed without anti-depressants, but I (the caregiver) only just got off the St. John's Wort I was taking to manage life in general. Of course, Alex should discuss with a doctor whatever he takes, but in general anti-depressants will flatten your emotions, and reduce your libido. My little happy herb takes a couple of weeks to kick in; it can be dangerous - issues with diabetes - and anyone thinking of it should clear it with a doctor (I did).
One of the hardest things with anti-depressants is that people are resistant to them when they should not be - "it's bad to use a crutch." Well, its not bad to use a crutch if you need one, but the term is now a negative one. Maybe think of it as an ankle wrap - helps to support you while you heal.
Best wishes to you and Alex!