The main difference between 「がち」and ぎみ is that 「がち」usually describes a general tendency in someone or something while 「ぎみ」describes a visible indication of a tendency. e.g. 1 田中は最近太りがちだ Tanaka has a general tendency to gain weigh but is not necessarily overweight at the moment of speech。Compare with; ２）田中は最近太り気味だ Tanaka is showing signs of being overweight。 Also 「がち」Cannot express the idea of "a touch of" or " a little". (taken from the Intermediate grammar dictionary)
So what is the difference between 「がち」and 「ぎみ」？
Yes I am also interested in this question above, it seems right to me. 彼は哀しい気味です。He tends to be a bit sad -ish. i know it's not correct English, but people still use "ish" to make words. Can it be used in this way with 気味？
how would you say 'I tend to slack off at work'? (is this ok?「仕事やってるときに怠け者気味です」)
expresses a feeling that, although not serious at the moment, there seems to be a sign of or a tendency toward a particular condition, as in, feeling a cold coming on or sensing that one is a little overweight (see my examples above).
Formed from verb-masu base + gimi or from noun + gimi Vm = Verb -masu base N = noun