WORD FOR THE FEELING OF DREAD/COMPLACENCY THAT COMES WHEN STARTING SOMETHING NEW (some combination of dread, complacency and intimidation that causes a person to freeze--TAGS: [meaning] [word-choice] [adjectives] [vocabulary])
Due to the wording of your request all single-word answers must reference either the “intimidation” or the “inertia” factors of your request (INTIMIDATION aspect: trepidation; the newly-minted “archophobia”; INERTIA aspect: lassitude; enervation; torpor; neurasthenia), because no single word in the English language combines these divergent qualities.
Additionally, if "laziness" is not a factor (and, based on personal experience with this issue, I agree that it is not) because it would "suggest not wanting to start" then "complacency", the feeling of smug or uncritical satisfaction with oneself or one's achievements, is also not a factor for consideration.
1. lack of vitality; "an enervation of mind greater than any fatigue"
2. serious weakening and loss of energy
3. the depletion or sapping of strength or energy;
Usage Note: Sometimes people mistakenly use enervate to mean "to invigorate" or "to excite" by assuming that this word is a close cousin of the verb energize. In fact enervate does not come from the same source as energize (Greek energos, "active"). It comes from Latin nervus, "sinew." Thus enervate means "to cause to become 'out of muscle'", that is, "to weaken or deplete of strength."; see The Free Dictionary enervation and Google enervation
While your official selection, “lassitude”, is certainly a gorgeous word, and both “lassitude” and “enervation” effectively evoke the weakness, diminished energy, and depleted vitality OP seeks, “enervation” possesses two qualities which, to my mind, recommend it over all other single words offered: 1. “enervation” includes the sense of dynamic process, of becoming or increasing, whereas all other suggestions describe a static condition, or feeling. 2. “enervation” possesses a verb and adjective form (ENERVATE verb: to weaken or destroy the strength or vitality; ENERVATING adjective: causing one to feel drained of energy or vitality) which would allow you to gracefully combine the “dreadful” aspect of your request with “enervation,” i.e., “the trepidation which enervates and saps the vigor necessary...” or "the enervating dread forestalling your initiative".