You and your doctor should be aware of these and you should get help if you are worried. Psychological problems are common after many types of surgery but these are rarely discussed. And it's not just the patients themselves who are affected - relatives and friends may have issues to work through, fears for their loved ones and irrational concerns. Firstly there may be a transient depression that can be very intense for some patients. This may be related to the anaesthetic drugs used, which can include powerful barbiturates to induce sleep.
Surgery is also a very stressful event, especially if done in an emergency.
The intensity of the experience and the threat to life that the operation and illness may have posed often make people do some serious thinking about the priorities in their life. The initial depression often wears off within a day or two, but sometimes disturbed feelings last longer. After major surgery it can take months for emotions to get back to normal. Don't be afraid to talk to the medical team, or your family, if you feel low. The impact of the illness itself can also raise all sorts of emotional issues.